Shape of Antarctic ice surface. Credit: BBC News

A detailed analysis of Antarctic ice data measurements comprised 50 years of exploration show that the White Continent contains about 26.5 million cubic km of ice. These numbers come out of an international project known as Bedmap2, which is a second attempt to reconstruct the ice thickness map of Antarctica. In recent years, satellite based observations provided us with a very good assessment of the height of the ice surface.

I would like to discuss one method that could be adopted for space exploration and could be used to estimate the thickness of ice mantle on extraterrestrial planets, on Ceres and other bodies in the main asteroid belt, and on Jovian moons.

This is the Passive Radio [frequency] Ice Depth Experiment (PRIDE) from JHU APL (Miller, Schaefer, and Sequeira, 2012). PRIDE is a passive receiver of a naturally occurring signal generated by interactions of deep penetrating Extreme High Energy (EHE) cosmic ray neutrinos( > 10^18 eV).

An illustration of the PRIDE concept. A high energy cosmic ray neutrino penetrates the ice at a grazing angle. The neutrino initiates a shower of secondary charged particles (the Askaryan effect, 1962) that emit a conical pulse of Cerenkov radiation that can be detected at satellite altitude. The distributions of the characteristics of detected pulses will indicate the thickness of the ice layer. Figure credit (Miller, Schaefer and Sequeira, 2012)

EHE cosmic ray neutrinos is a product of the interaction of cosmic ray protons with cosmic background radiation. These neutrinos could penetrate deep into the ice and interact with hydrogen nuclei. These interactions produce a shower of particles that generates Cherenkov radiation. This radiation is then detected by the PRIDE instrument.

For the given conditions (water ice, T 50-140 K), the spectrum of emitted radiation peaks at 0.2–2 GHz. This radiation could be detected from orbit.

This concept is especially useful for long missions going to Jupiter moons or to the asteroid belt because it employs a passive remote sensor. The instrument registers event rate, amplitude and direction of each event for EHE cosmic ray neutrinos with energies 10^18 – 10^19 eV. At this energies, the detectable signals with SNR>5 could be registered at satellite altitude 100-500 km and be able to measure ice thickness ranging from 10 to 100 km.

a strawman PRIDE antenna array for full 360-degree azimuthal coverage. The two rings of antennas are offset both vertically and horizontally to enable reconstruction of event direction via timing differences in neighboring receivers; b – angular acceptance. Credit -Miller, Schaefer, and Sequeira (2012).

The antenna design is based on commercially available flanged horn antenna. For using on a spacecraft some modifications need to be made to reduce its thickness and also to make it shorter and wider. Ideally, the array of 8 antennas collected in 2 rows is needed for 360-degree azimuthal coverage. This allows:
- measuring both zenith and azimuth reconstructing with 1-2° zenith angle accuracy;
- each event to be registered by two or three antennas.

There are some concerns regarding the noise that could bias the measurements. The receiver temperature is expected to be ~ 140 K, so it will contribute to thermal noise. However, authors expect “that the receiver noise can be reduced so that the local ice will again be the limiting factor”. The estimated signal-to-noise ratio (SNR) due to ice noise is expected to be ~10 at 100K.

Local RF noise from Jupiter environment comes in forms of bursts at frequencies of tens MHz. Also there is a thermal emission from Jupiter and noise due to synchrotron emission from electrons in Jupiter’s magnetosphere. According to authors, synchrotron emission “produces much less noise than the burst or thermal emission sources do at higher and lower frequencies, and matches the same range of 0.2–2 GHz that is optimal for both Cerenkov emission and ice transparency”.

The short radio bursts might also turn false triggers, but they have the spectral characteristics different from Askaryan-Cerenkov bursts.

Because PRIDE is a passive receiver it doesn’t require additional resources such as power, cooling, etc. The instrument also doesn’t have moving parts. Antennas could be placed on the spacecraft body and any open locations. I believe that makes it a perfect instrument candidate for deep-space mission to explore the icy moons of Jupiter, like Jupiter Icy moons Explorer (JUICE). I hope they hear me at ESA.

References:

Antarctic ice volume measured -http://www.bbc.co.uk/news/science-environment-21692423

Askaryan, G.A., 1962. Excess negative charge of an electron–photon shower and its coherent radio emission. Sov. Phys. J. Exp. Theor. Phys. 14, 441–443.

Barwick, S.W. et al., 2006. Constraints on cosmic neutrino fluxes from the ANITA experiment. Phys. Rev. Lett. 96 (171101), 1–4.

Carry, Benoit; et al. (November 2007). “Near-Infrared Mapping and Physical Properties of the Dwarf-Planet Ceres”(PDF). Astronomy & Astrophysics 478 (1): 235–244.arXiv:0711.1152. Bibcode 2008A&A…478..235C.doi:10.1051/0004-6361:20078166.

Miller, Schaefer, Sequeira, PRIDE (Passive Radio [frequency] Ice Depth Experiment): An instrument to passively measure ice depth from a Europan orbiter using neutrinos, journal homepage: www.elsevier.com/locate/icarus, 2012

Miller, T., Schaefer, R., & Brian Sequeira, H. (2012). PRIDE (Passive Radio [frequency] Ice Depth Experiment): An instrument to passively measure ice depth from a Europan orbiter using neutrinos Icarus, 220 (2), 877-888 DOI: 10.1016/j.icarus.2012.05.028

Varner, G., 2003. Self-Triggered Recorder for Analog Waveforms v. 3 (STRAW3) Data Sheet. Dept. Of Physics, University of Hawaii.

The area possibly affected by meteorite. Credit: BBC News (http://www.bbc.co.uk/news/world-europe-21468116)

(Terminology: A bolide is an extraterrestrial body ranging in size from 1 to 10 km across that hits Earth at velocities faster than a speeding bullet. Meteors are pieces of space rock, which enter the Earth’s atmosphere. Many are burned up by the heat in the upper atmosphere. Those that survive and strike the Earth are called meteorites.)

According to the Russian Academy of Sciences the meteor estimated weight was about 10 tons and it entered the atmosphere at the speed of ~ 54,000 km/h. When the meteorite hits the Earth’s atmosphere at that speed it is like hitting the wall. That releases a huge amount of energy, which is comparable with the huge bomb explosion. The meteor shattered in the upper atmosphere about 30-50 kilometer above ground, creating the strong sound waves and showering the region with smaller debris that caused damage over a wide area. It released the energy of several kilotons above the Chelyabinsk region and broke about 1 million square feet of glass, according to the city official’s estimate.

A powerful blast rocked Cheliabinsk region (Russia) of Ural mountains early on Feb 15, 2013. Bright object is identified as possible meteorite. Credit: times.uk

As a result of the shock waves caused by the blast, ~ 270 buildings in Cheliabinsk have sustained damage and ~ 1000 people reported to hospitals seeking for treatment said Vladimir Stepanov, of the National Center for Emergency Situations at the Russian Interior Ministry. Hospitals, kindergartens and schools are among those affected. As RIA Novosti reported, about 20,000 emergency response workers have been mobilized.

Thanks’ to smart phones and dashboard cameras so popular in Russia, the event was widely captured on amateur video. Some videos showed a bright object speeding across the morning sky, leaving a thick white contrail and an intense flash.

Russian police looking for meteorite pieces. Credit: RT.com

A large meteor fragment was seen landed in a lake outside of Chebarkul, a small town in Chelyabinsk region (BBC Russian).

It is early to tell anything about the meteorite size and composition. We could only provide estimation. As Don Yeomans, head of NASA’s Near-Earth Object Program, told SPACE.com -”If the reports of ground damage can be verified, it might suggest an object whose original size was several meters in extent before entering the atmosphere, fragmenting and exploding due to the unequal pressure on the leading side vs. the trailing side.”

Other bolide explosions over Siberia in the past 100 years

Such meteor strikes are rare and luckily happen in uninhabited areas where they don’t cause damages and injuries to humans. A similar one – Tunguska meteorite – hit Siberia in 1908 (~ 100 years ago) and devastated an area of more than 2,000 sq km.

On 26 February, 1984,  a huge Chulym bolide exploded above the Chulym river, Siberia (57.7N; 85.1E)

The last even on the similar scale – Vitim event or Bodaybo event  – occurred in 2002. It is believed to be an impact by a bolide in the Vitim River basin. The event occurred near the town of Bodaybo in, Siberia, on September 25, 2002 at approximately 10:00 p.m. It was also detected by a US military missile-defense satellite.

Asteroid 2012 DA14

Interestingly enough, this collision took place as the world waited for February 15th, close pass of asteroid 2012 DA14. According to both the European Space Agency and NASA, no link between the two events is thought possible, but we will see.

For the information on how to watch asteroid 2012 DA14 online, refer to Alan Boyle posting (Science Editor, NBC News)

Venus transit, June 05, 2012, credit NASA

It is today, on June 5, 2012. It starts at sunset on East Coast (actually at 2 PM). Venus will pass across the upper portion of the sun. The next time it will occur in 2117. I am afraid I would be too old to enjoy it. The last time it occurred on June 8, 2004 and that time Venus passed across the lower part of the Sun. This time it goes across the upper portion of the Sun.

Venus transit on June 08, 2004, credit SPL

See pictures from the last event here.

And I am unprepared. I gave away the last pair of my sun viewing glasses and my Welding filters are all gone.
Transit visibility map (credit NASA) is here.

June 5, 2012, Venus transit observation times. Figure credit Daily Mail

What to do if you are unprepared for this event

• Read this page on how to safely observe the Sun.
• If you are not equipped, PLEASE do not take any chances! Review this page.
• You can easily destroy your equipment or even your eyes. I will content myself with watching the live NASA stream.
• If you have a binoculars or a small telescope, and that is all what you have, you can project an image of the Sun through a telescope or binoculars onto a white screen – paper plates, walls and sidewalks – whatever white surface you have. More guidance is provided on this page, read it carefully - Do it yourself.
• You can watch NASA web cast from Mauna Kea, Hawaii. This webcast event will run through the whole transit, beginning 5:45pm EST. You can view the webcast by finding Hawaii on the Google map on the page.

History of observations

The Venus transit was observed only seven times in the telescopic age: in 1631, 1639, 1761, 1769, 1874, 1882 and 2004. The first time it was recorded in 1639 by a young English astronomer Jeremiah Horrocks in Much Hoole, who lived in a tiny village in the north of England. He watched it using his small telescope.

There are 2 good articles describing the history of observations of Venus transits

1. Venus to put on Sun spectacular, by Jonathan Amos on BBC.
2. Pimple on the sun that spells a spot of bother by Daily Mail.

Why do we think that Population III stars exist?

The term “Population III” could be assigned to two types of stars: “1) the ones which form out of the pristine gas left over after cosmological nucleosynthesis and generated the first metals; and 2) the ones which have been hypothesized to provide the dark matter in galactic halos” – Carr (CarrCaltechWeb 2012).

The first type definitely exists, since we have metals in our disposal, and we know that elements heavier than H and He could only be generated through stellar nucleosynthesis. The second type, however, not necessarily exist, because first galactic halos could also be made of some ancient pre-atomic particles. I am going to discuss the first type of Population III stars.
Note that both types of Population III stars might have formed during the first phase of galaxy formation or even before first galaxies were formed.

What kind of information do we have about early ages of the Universe?

WMAP provides us with the information of state of the Universe up to 400 000 years after the Big Bang by measuring the temperature anisotropies in the cosmic microwave background (CMB). By observing the Universe in all different wavelengths (radio, infrared, µv, visible, x-ray, gamma-ray, etc.) we can get even information about the early Universe up to z ~ 10 .

The first stars are believed to be formed at redshifts z ~20 – 30. But how exactly they have been formed; their masses, lifetimes and luminosities are still subjects of a constant debate.

The cosmic timeline as it appears in the work of Bromm & Larson (2009)

Lambda-CDM model

According to the Lambda-CDM model (ΛCDM), the first star-forming regions (or protogalaxies) appeared 100—250 million years after the Big Bang. They had masses of 10^3—10^6Msun and dimensions of 30—100 ly. They were made mostly of a mix of dark and baryonic matter. The segregation between those two would come later.

Computer simulations show that the early cosmic structure evolved from the density fluctuations (nodes) in primordial matter. The small density fluctuations appear first, and then they grow through two processes 1) by merging with other fluctuations, and 2) by accretion matter due to gravity. Primordial gas would gather around these nodes creating bigger and denser clouds. At a certain point, some of gas clouds started contracting under their own gravity and then collapse.

During the collapse, the temperature of baryonic matter raised due to compression heating. For a minihalo mass 10^6 Msun at z~ 20 Tvirial is estimated to be ~ 8000 K (Bromm and Larson 2004, 2009; Bromm 2012). At these temperatures some lonely hydrogen atoms meet and made hydrogen molecules (H2).

What is the probability that a certain density fluctuations would grow big enough?

Bromm (2012) presents the calculations of how density perturbations grow in time following the proportionality D(z) ~ 1/1+z, where z is a redshift and D is the growth factor. As we could see, D(z) is really small at high z, but it grows as z decreases. That means that some of density fluctuations could grow big enough over zs to become the first star forming sites. In the same paper, Bromm (2012) also introduced the important parameter (called over-density or sigma) that defines the probability that at the given redshift the density of a given region of primordial gas is above an average density of nearby Universe by a given value. The growth of a single density fluctuation becomes non-linear, when sigma approaches 1. At this point, the nearby dark matter (DM) collapses, taking baryonic matter with it. For a protogalaxy with a minihalo mass ~ 10^6 Msun to start a runaway collapse at z=20, its sigma should be ~ 1.7, which means that at z~20 the star forming spots were rare, but “not so rare that we should eliminate them from the theory” – Bromm.

Molecular hydrogen and separation of dark and baryonic matter

Cooling rate of primordial gas as a function of temperature. The solid line represents the contribution from atomic hydrogen and helium and the dashed line represents the contribution from molecular hydrogen. At temperatures below 10^4 K cooling is provided by H2, which is a poor coolant, but at T> 10^4 K more efficient atomic hydrogen line cooling comes to play. Courtesy: Bromm (2012).

The primordial gas needs to cool in order to star formation to start. The major mechanism that cools primordial gas right after Big Bang is the excitation of resonance lines of atomic hydrogen and helium. It was enough to cool the gas to the temperatures of ~ 10^3 – 10^4 K. In order to cool below Tvirial, the gas must form molecules of hydrogen, whose rotational excitation allowed it to cool to T~200 K (Abel et al. 1997).

At temperatures of T > 10^4 K atomic hydrogen line cooling is very efficient, whereas at lower temperatures, cooling mainly relies on H2, which is a less efficient coolant.

The cooling of molecular hydrogen played the major role in star formation. It allowed the baryonic matter to separate from the dark matter. It worked the following way: H2 molecules would emit radiation, lose energy and then gather together and form a proto-disk, while dark matter particles would remain scattered in the primordial gas cloud.

This happens because dark matter only reacts on gravity and does not emit or accept radiation. The best analogy that comes into my mind is a separation of oil and water. Imagine (or just do it in your kitchen) that you are putting several drops of oil into a glass of water. They would stay separated for some time, but eventually (especially if you introduce some disturbances by shaking/rotating the glass) they would gather into bigger drops and finally form a single one, which would stayed separated from water.

Over a period of time, the structure resembling a galaxy forms with a disk made of H2 and He and a dark matter halo. Inside the gaseous disk, the local inhomogeneities would grow and eventually form big clumps. Some of them grow so big that they would collapse under their own gravity. When a clump begins to collapse, its density raises. That in turn, also raises the gas temperature and therefore slows the clump contraction down, so it needs to gather more mass to star collapsing again. Bromm & Larson (2004, 2009) have shown that the masses of the star-forming gas clumps could reach masses of 500 – 1000 Msun. Some of these clumps would undergo the runaway collapse and form the first stars (Loeb 2010; Bromm 2009, Bromm, Kudritzki, Loeb 2001).

The first stars

The general notion is that Pop III stars followed the same paths as same physics in their development as Pop I and Pop II stars. The general theory of star formation considers 3 basic mechanisms – gravitational instability, proto-stellar accretion and properties of initial mass function (IMF).

Gravitational instability could be explained in terms of Jeans mass (Mj) and Jeans length (Lj). Since a primordial gas cloud contained mainly molecular H and He, “the physics of the hydrogen molecule” rather than cosmological conditions, are considered to play an essential role in primordial gas collapsing and formation of the first stars (Bromm and Larson 2004).

Therefore, the Jeans mass equation can be used to estimate a critical mass for a primordial gas cloud.
Mj describes the equilibrium between the inner pressure of the gas cloud (due its temperature) and the gravitational force. The first one makes a cloud inflate and the last one makes it collapse. The inner pressure in primordial gas was similar to the present day molecular clouds, but the temperature was ~ 200 K, which is much higher ( ~100°K in the outer layers of present day molecular clouds and 10°K in the cores of molecular clouds) (Bromm & Larson, 2004, 2009).

It defines the minimum mass that a clump of an ideal gas must have in order to collapse under its own gravity

Mj= ρ Lj ^3 ~ 500 Msun (T/200K)^ 3/2 (n/10^4) or

Jeans mass

Where ρ is the density of hydrogen, n~ρ /mH is its number density, and the normalization coefficients are introduced to reflect the typical values in Pop III star forming regions (Bromm 2012).

Another condition – the Jeans length – is based on assumption that in runaway collapse the sound crossing time tsound (for a sound that moves in a media with a given density) should exceed the free fall time.

Both equations for Jeans mass and Jeans length produce the similar result of mass estimate of ~ 100 Msun.

Accretion: The current notion of star formation is that every star (Pop I, II III) grows from inside-out and a small core is formed first at the center of a gas cloud, and then it grows through accretion (Bromm 2009).

How the core is formed?

Runaway collapse due to gravitational instability could proceed as long as the gas is able to radiate away the heat due to compression. After a certain density threshold, the gas cloud becomes optically thick – or that H2 molecules start to collide with other atoms/molecules before they even have a chance to emit an infrared photon.
That makes the further cooling impossible. That is the moment when a thermal pressure stops the collapse and a protostellar core is born. After that the star grows through accretion. Current estimate for a proto-stellar core mass is ~ 10^-2 Msun (Bromm & Larson, 2004, 2009; Bromm 2012).

There are two types of accretion mechanisms that could be found in stars – spherical and disk accretion.
Spherical accretion dominates at early stages, but over time, as the proto-star gains more material with some angular momentum, a proto-stellar disk forms. Then, accretion is shifted to a disk mode.

The key assumption for the spherical accretion rate is that gravity cannot move any baryonic matter faster than its free fall speed, which is close to the speed of sound cs in a given media with given temperature and density. And cs is proportional to the square root of the temperature.

• For Pop I stars the temperature of the interstellar media (ISM) is ~ 10K that makes the accretion rate ~10^-5 Msun per year.
• For Pop III stars, the ISM temperature was 300K and the accretion rate was 10^-3 Msun per year. In order to cool to the present day molecular clouds temperatures, the gas must have more effective cooling agents such as metals and grains of dust, which were not available yet.

Here we see the difference in 2 magnitudes, which explains why Pop III stars were so big.

The disk accretion is proportional to the gas viscosity and mass density (Clark et al. 2011). Both mechanisms give us the accreting mass of Macc ~ 10^-3 Msun per year. Accretion of a massive stars follows the Kelvin-Helmholtz timescale, which gives us the time estimate of 10^5 years and results in an upper limit for the Pop III star mass of 100 Msun. The real masses would be smaller, due to the various negative feedbacks from the growing protostar that would stop accretion at some point (Stacy et al. 2012).

Initial Mass Function

Zero-age main sequence (ZAMS) for very massive stars, shown for Pop III (left line) and Pop I stars (right line). Stellar luminosity shown in Lsun is plotted vs. effective temperature (in K). Stellar masses are represented as diamonds along the sequence, from 1000 Msun (at the bottom) to 1000Msun ( at the top). In shows that the Pop III ZAMS is shifted to higher values of effective temperature, asymptotically reaching Teff ≃ 10^5 K. Figure and caption adopted from Bromm et al. (2001). Current estimates for the Pop III mass however shifted to smaller values.

Initial mass function (IMF) is an empirical function that describes the distribution of stellar masses immediately after star formation. Current estimates for an average mass for a Pop III stars are stirring down from a very high mass up to 300 Msun (Abel et al. 1997) to 100—200 Msun (Bromm and Larson 2009), to even lower values of few dozens of Msun (Bromm 2001, 2012).

How exactly massive first stars were?

The most important property of a star is its mass. If we know the mass of the star, we could estimate its temperature, luminosity, lifespan, and also effects it produces on its environment. That’s why it is so important to estimate how massive the first stars were. However, precise estimates are difficult to provide because of the various scenarios that could occur during the stages of star formation.
For example:

The initial gas could may not fragment at all and create one huge star that eventually consumes all the gas around (Abel et al. 1997). Or it might miss the star formation stage and collapse directly to a black hole (Johnson et al. 2008).

Or it could fragment and form multiple moderate stars instead of a single big one. There is still probability that the fragments would be also big (the H2 cooling keeps the Jeans mass high) and form binary system. Bromm and Larson (2004, 2009) demonstrated that Population III star formed in such binaries could accrete ~ 50Msun in first 10,000 years, making final mass of 100—200Msun.

Or the angular momentum of the collapsing cloud could produce a combination of small and bigger stars, where smaller stars move around a central massive star. Turk, Abel and O’Shea (2009) have shown that multiple fragmentations were possible in the protostellar disks resulting in that “a substantial fraction of Population III stars are forming binaries or event multiple systems”.

Stacy et al (2010) simulate the accretion mechanism of the central protostar for 5000 years after its formation. The initial core was represented as a sink particle with adding some essential detail from accretion physics, including rotation, density, and gas chemistry. The result was a small multiple system “dominated by a binary with masses of 40 and 10Msun” – Stacy et al. If the first stars were born in multiple systems, the old model depicting a fat lone Pop III star living in isolation and disappearing in SNe should be modified. This would also affect the expected feedback from the first stars and their observational signatures.
However, due to computational difficulties, none of the above groups was able to proceed with simulations to the point where the actual stars were born.

Some studies suggest that early stars were rapidly rotating with a speed up to 1000 km s−1 which is close the star’s break point (Stacy et al 2010, 2011; Chiappini et al 2011). That means that strong rotational mixing could have impacted their structure and nucleosynthesis with possible outcome in hypernova explosions and gamma ray bursts (GRBs). Well, in that case we could search for distant GRBs and signatures of early hypernovae as a proof of existence.

Two generations of Pop III stars?

There is also a possibility that two generations of Pop III stars actually existed – both made from the same metal-free gas. Very massive (1000 Msun) PopIII.1 stars formed first and less massive Pop III.2 stars (40—60Msun) formed later (Johnson et al. 2008).

How could that happen?

High massive Pop III stars were very hot and luminous. They radiate in UV, creating a large amount of energetic photons, as well as winds and shock waves. This feedback would ionize the neutral H and He around and outside their DM halos creating large H II regions. This results in formation of a large fraction of HD molecules. HD could cool the gas much more efficient that H2, down to 40– 50 K. At such low temperatures, restrictions due to Jeans mass would relax, allowing formation of less massive stars of ∼50Msun. These less massive Pop III stars formed (close to the end of life of Pop III.1s) in ionized but still metal-free primordial gas. These were named “Pop III.2” stars (Johnson et al. 2008; Ohkubo et al 2009). Note that both Pop III.1 and Pop III.2 coexisted for some period of time.

Not the end of story

So it looks like that first stars may had come in different shapes and flavors. And that is good, because if more various they were more chances we have to catch (eventually) at least some of them.

References

Abel, T., Anninos, P., Zhang, Y., & Norman, M. L. 1997, NewA, 2, 181

Bromm V. The First Stars and Galaxies – Basic Principles, 2012 -http://arxiv.org/pdf/1203.3824.pdf

ResearchBlogging.org, & Bromm V. and Larson R (2004, 2009). The First Stars in the Universe Scientific American

Bromm, V. (2010). The Very First Stars: Formation and Reionization of the Universe Proceedings of the International Astronomical Union, 5 (S265) DOI: 10.1017/S1743921310000116

Bromm, V., Kudritzki, R. P., Loeb, A. 2001, ApJ, 552, 464

CarrCaltechWeb – http://ned.ipac.caltech.edu/level5/ESSAYS/Carr/carr.html, assessed on May 24, 2012

Chiappini C. et al., Nature 472, 454 (2011)

Clark P. C. et al., Science 331, 1040 (2011)

Johnson, J. L. & Bromm, V. 2006, MNRAS, 366, 247

Johnson, J. L., Greif, T. H., & Bromm, V. 2008, MNRAS, 388, 26

McKee C. F. & Tan, J. C. 2008, ApJ, 681, 771

Ohkubo T., Nomoto K., Umeda H., Yoshida N. and Tsuruta S., EVOLUTION OF VERY MASSIVE POPULATION III STARS WITH MASS ACCRETION FROM PRE-MAIN SEQUENCE TO COLLAPSE, The Astrophysical Journal 706 (2009) 1184, doi:10.1088/0004-637X/706/2/1184

Santoro Fernando and Shull Michael, CRITICAL METALLICITY AND FINE-STRUCTURE EMISSION OF PRIMORDIAL GAS ENRICHED BY THE FIRST STARS, The Astrophysical Journal, 643:26–37, 2006 May 20 http://iopscience.iop.org/0004-637X/643/1/26/pdf/0004-637X_643_1_26.pdf

Stacy, A., Greif, T. H., Bromm, V. 2012, MNRAS, in press (arXiv:1109.3147)

Stacy, A., Greif, T., & Bromm, V. (2010). The first stars: formation of binaries and small multiple systems Monthly Notices of the Royal Astronomical Society, 403 (1), 45-60 DOI: 10.1111/j.1365-2966.2009.16113.x

Stacy A, Bromm V, Loeb A, Mon. Not. R. Astron. Soc. 413, 543 (2011)

Stacy, A., Bromm, V., & Loeb, A. (2011). Rotation speed of the first stars Monthly Notices of the Royal Astronomical Society, 413 (1), 543-553 DOI: 10.1111/j.1365-2966.2010.18152.x

Tan J., Population III stars: formation, feedback and evolution of IMF, Proceedings IAU Symposium No. 255, 2008 DOI: 00.0000/X000000000000000X

Turk M.J., Abel T., O’Shea B., Science 325, 601 (2009); [MEDLINE]

The space shuttle Discovery in Bethesda, MD sky on its final flight. Picture courtesy #spottheshuttle

We captured the space shuttle Discovery as it passed over Bethesda, MD to its permanent location at the Smithsonian’s annex in northern Virginia. Discovery is the fleet veteran with 39 orbital missions. And it is the first of the three retired space shuttles scheduled to go to a museum. And this is sad. I am glad I saw it flying over NIH. But it reminded me the scene from “Lord of the Rings” where elves were leaving Middle Earth. Something good – a big dream - is leaving us now.

This morning the shuttle was photographed piggybacked by Boeing 747 and was about to land at Dulles International Airport.
More about this story on Fox News…

More beautiful pictures from “The Guardian” – it looks old and tired.

The space shuttle Discovery flying over Godard Space Center. Picture courtesy: Laura McDonald

On Monday, April 23, NASA’s 747 Shuttle Carrier Aircraft with space shuttle Enterprise mounted atop will fly over the New York City. Read more from the NASA site…

Letter: What Discovery’s last flight means for us.

Here is the drawing. It shows the hat in a river (after Moomin-mama and Moomin-papa dropped it into the river) and canary birds which were fish and get transformed after they swam into the hat.

The Wizard Hat in a river with fish and canary birds. Figure credit: OV

A sky map for Lyrid meteors, April 2012. Image credit: space.com

The Lyrid Meteor Shower peaks at April 21-22 night, the best observing time is from midnight to dawn April 22. It happens at the new Moon, so moonlight would not spoil observations. This year NASA estimation is ~ 15 meteors per hour at the peak, but the number could vary. Observations made after 1 am are expected to be the most productive. The Lyrids meteors have been observed for at least 2,600 years.

Full Moon is on the 7th and Last Quarter is on the 13th. The new Moon appears on the 21st and the First Quarter on the 29th. On April 7th, the Moon appears between Saturn and Spica . And on April 10th evening, it will be very close to the Antares.

April 24, 2012, observing Venus and crescent Moon. Image credit: Stellarium/IM

On April 24th after sunset, we might be able to see Venus at magnitude -4.6 above a thin crescent Moon. The same time is good to look for the “earthshine” illuminating the “dark side” of the Moon – often called the “old Moon in the new Moon’s arms”.

Every 8 years, Venus passes close to the Pleiades Cluster making a very nice picture. This year, it April 8th and Venus passes at the low left side of the brightest stars in the cluster.

The Moon- an image of Alpine Valley region. Image credit: Jorellbank web

The Moon - Alpine Valley region map

April 12th and 29th is a good time to observe the Alpine Valley region of the Moon if you have a small telescope.
Mars is in the evening sky, being due north at 9pm. Close to Mars is the blue-colored Regulus, from the constellation of Leo. On April 30th, after 9 pm, a 9 day old Moon will be seen just below the disk of Mars lying close to Regulus in Leo.

In April, Jupiter is sinking into the twilight and after the 20th, it will be difficult to locate.

Saturn is now rising in the southern sky in the constellation Virgo during the evening and will lie due south around midnight (UT) when at opposition on April 15th. The planet’s North Pole is tilted towards us, making Saturn rings easy to see in a small telescope and even in binoculars.

ISS
Use the link below to find when the space station(ISS) will be visible in the next few days in your region. The NASA website provides details for several cities in USA and across the world too.

These five rockets will release an aluminum based chemical into the upper layers of atmosphere (the mesosphere) that will form milky-white clouds that will trace winds in space. These clouds might be visible for public up to 20 minutes by East coast residents from southern parts of New Hampshire and Vermont till South Carolina.

The launch window for March 15, 2012 is scheduled between midnight and 1:30 a.m. EDT. The backup launch days are March 16 through April 3. For more information, refer to the NASA Wallops page at http://www.nasa.gov/centers/wallops/news/12-03.html.

The map of the mid-Atlantic region of the U.S. shows the projected area where the rockets may be visible while the motors are burning through flight. It also shows the flight profile of each of the five rockets. Credit: NASA/Wallops

Why studying the mesosphere is so important?

The mesosphere is a layer of Earth's atmosphere. The mesosphere starts at 60 km above Earth's surface and goes up to 100 km high. Image credit: Windows to Universe

The mesosphere is the layer of the Earth’s atmosphere that is directly above the stratosphere and directly below the thermosphere. It is located above stratosphere and below thermosphere occupying a layer from 60 km to 220 km above Earth’s surface. ~ 40 tons of meteors typically enter the mesosphere per year. Most of them dissipate giving away iron and other material, which creates a refractory layer there.

This region is also known for having strong zonal East-West winds which fly with speeds up to 500 km/h. The high-altitude winds in the mesosphere were first discovered in 1960s. Current studies confirm their connection to the complicated electrical current patterns that surround Earth, but it needs a further investigation.

The other atmospheric phenomena such as tides, gravity waves and planetary waves are also present in this region. Most of these tides and waves are actually excited closer to Earth – in the troposphere and lower stratosphere, but they propagate upward to the mesosphere. In the mesosphere, their amplitudes grow so large that waves become unstable and dissipate, which in turn deposits kinematic energy (momentum) into the mesosphere and, according to one theory, this creates high winds and largely drives global atmospheric circulation.

In order to figure out what drives these high winds and how atmospheric disturbances in one hemisphere could influence weather in the other, scientists must get an understanding of how these winds move and what kind of turbulence they show.
One possible kind of turbulence which could be found in these winds is so- called 3D turbulence. If you imagine water which is flowing down a rocky river and swirling with small ripples around rocks or gusting winds on Earth moving falling leafs around, that is 3D turbulence.

The theory suggests that the upper level jet streams are moving following laws implied by 3D turbulence, and therefore they can be modeled similar to small-scale waves in water. Such waves in the mesosphere might arise due to heat in the lover atmosphere that varies in the course of a day.
On the other hand, studies show that the winds at that altitude are flying way too fast to fit with the small-scale wave’s model.

“This area shows winds much larger than expected,” says Miguel Larsen, a space scientist at Clemson University, who is the principal investigator for the Anomalous Transport Rocket Experiment (ATREX).

Moreover, if the small-scale wave’s model were correct, the man-made tracers and satellites’ debris, which happen to enter the mesosphere (e.g. Space Shuttle debris) should have broke up and dissipate due to high turbulence, but they did not.

So to get a better view of what is going on in the upper layers of Earth’s atmosphere, NASA designed the ATREX experiment. It will help us understand “the big question about what is driving these fast winds” said Miguel Larsen.

Challenges

Because the mesosphere is located lower than the Earth’s low orbit where it can be studied using satellites, but still higher than where most planes fly, it is difficult to probe.

However, this location makes it a perfect target for the sounding rocket experiment. A sounding rocket, which is also called a research rocket, is a rocket that carries scientific instruments and designed specifically to perform experiments during its sub-orbital flight, which usually takes between 5 and 20 minutes. The instruments the rocket carries use this time to take measurements and to send data back to Earth.

For more information, see References for the NASA sounding rocket report, 2011.

The ATREX experiment

The ATREX experiment comprises 5 sounding rockets, which will launch at once from Wallops NASA center. They will follow specific timing and direction to gather the required data.

These rockets are scheduled to launch on one clear night between March 14 and April 3. The clear night skies are also required at three camera sites located along the coast in Virginia, North Carolina and New Jersey.

The launch date is set for March 15 is between midnight and 1:30 a.m. EDT. The backup launch days are March 16 through April 3.

The red dots over the water show where ATREX will deploy chemical tracers to watch how super fast winds move some 60 miles up in the atmosphere. While there are only five rockets, two will deploy two sets of tracers, resulting in seven clouds. Only six dots appear in this image, since two will be deployed at the left-most red/green dot, which represents Wallops. Three cameras will track the cloud tracers – one at Wallops and two located at the green dots. Credit: NASA/Goddard Space Flight Center

The rockets will through a substance to create clouds in the lover mesosphere which could be traceable from the Earth. Scientists will then use special cameras to track the five clouds and measure how fast and in which directions they move away from each other.

This task is quite difficult though, because it requires 3D mapping of several spots in high atmosphere (100 km high) in only 20 minutes.

The chemical used to create clouds is called trimethyl aluminum (TMA). When dispersed, it forms milky, white clouds which can be traceable from the ground. So we could see them on East coast. These clouds will follow the winds in space and scientists will be able to track them with cameras. In addition, two of the rockets will have instrumented payloads to measure pressure and temperature in the atmosphere.

How to watch it

The map of the mid-Atlantic region of the U.S. shows the projected area where the rockets may be visible while the motors are burning through flight. It also shows the flight profile of each of the five rockets. Credit: NASA/Wallops

According to NASA, these clouds may be visible for up to 20 minutes by residents from South Carolina to southern New Hampshire and Vermont.

The NASA Visitor Center on Wallops island, VA will be open at 10 p.m. on March 14, 2012 for public viewing. Launch status also is available on the Facility’s Facebook page and its launch status line at 757-824-2050.

The mission will be web cast beginning at 10 p.m. on March 14, 2012 at:
http://sites.wff.nasa.gov/webcast

Mission status on March 14 can be followed on Twitter at:
http://www.Twitter.com/NASA_Wallops

More information on the ATREX mission is available on the Internet at the ATREX experiment page -
http://www.nasa.gov/mission_pages/sunearth/missions/atrex.html

References:

NASA Sounding Rockets Annual report 2011, http://sites.wff.nasa.gov/code810/files/Sounding_Rockets_Annual_Report_2011.pdf

Larsen, M. F., and C. G. Fesen (2009). Accuracy issues of the existing thermospheric wind models: Can we rely on them in seeking solutions to wind-driven problems? Ann. Geophys., 27, 2277–2284, doi:www.ann-geophys.net/27/2277/2009/, 2009.

On February 5th, 2012, the Russian team has finally managed to penetrate through almost 4000 m (3,768 m) of Antarctica’s ice and reached the surface of Lake Vostok.

The Russian science team, despite cold and limited money for scientific research, has been drilling down toward Lake Vostok for ~ 20 years now.

What is in the water there?

Antarctic map: lake Vostok

The lake is believed to be the largest of ~ 140 sub-glacial Antarctica’s lakes (250 km long and 50 km wide). Its overlying ice sheet provides a continuous climate record of the past 400,000 years, while its under-ice water might have been isolated from outside world for 15-25 million years.

Discovery

The idea of sub-glacial lakes was first proposed by Russian scientist (however largely known as anarchist and revolutionary) Pyotr Kropotkin. He proposed that the pressure exerted by the huge mass of Antarctic ice could be enough to raise the temperature at the bottom of the ice sheet to the melting point. This theory was later developed by another Russian scientist I. A. Zotikov. It was later confirmed that is also warmed by geothermal energy.

Lake Vostok. Sources: NOAA, Lamont-Doherty Earth Observatory. Marc Kaufman and Alberto Cuadra/The Washington Post

In 1964, Andrey Kapitsa after several years of seismic soundings research, suggested the existence of a sub-glacial lake in the region where soviet Antarctic station Vostok were located. That is how it gets its name.

In 1996, two teams of Russian and British scientists performed a combined research to define the lake shape and surface by combining a variety of data, including airborne ice-penetrating radar imaging observations and space-based radar altimetry.

Why this lake is so interesting?

There are several reasons why scientists are so much interested in probing the lake Vostok.

Lake Vostock schematic. Image credit: Rob Cooper and Thomas Durante

1. It is one of rare places which are still unexplored on Earth.
2. The lake Vostok presents the most extreme environment, as well as is the scientific work which is done there.
3. The 4km thick ice sheet that covers the lake has been accumulated and lay undisturbed for at least 420, 000 years. By examining this ice, we can reach for a unique and incessant climate record ever existed on Earth.
4. Scientists hope that studies of Lake Vostok and other sub-glacial lakes will advance knowledge of Earth’s own climate and help predict its changes.
5. Its under-ice water might have been isolated from outside world for 15-25 million years. After discovery of extremophily in 1980-1990, there is a possibility that a unique microbial life may be possible in the lake despite its harsh conditions (e.g. high pressure, cold, low nutrient input, high oxygen concentration and an absence of sunlight).
6. Microbiologists believe that the lake could offer a hint for unique life forms.
7. If life in Lake Vostok would be found and confirmed, we could hope for finding life on icy moons of Jupiter and Saturn (Europa and Enceladus).
8. The drilling technology developed and mastered on Lake Vostok can be later used for drilling on icy moons Europa and Enceladus.
9. It is believed that the search for evidence of life in samples from Lake Vostok has similar technical challenges and similar analytical procedures to those involved in the exploration of a sub-glacial ocean on Jupiter’s moon Europa.

Drilling

Challenges

Vostok Station is one of the coldest place on Earth (the temperature of -89 C was recorded in 1983). The current temperature, is about 40 C below zero; it is a late summer there and the Antarctic season is about to close. The drilling is slow, an average 50 m per season. In 2010, the expedition stopped somewhere 10- 50 meters short of the lake surface due to inclement weather and the scientists were forced to abandon the expedition. The contamination of the lake water due to drilling is another big problem.

Techniques

Deep ice core drilling at Lake Vostok (where the Vostok station located) began in 1970s, when a set of open holes were drilled using a thermal drill system suspended on cable. The deepest one reached 952.4 m in May 1972. Because temperatures on the Vostok Station are the coldest ever recorded on Earth (reaching -89C), the major problem was that the hole made by thermal drill get frozen very fast and then closed by new formed ice. Therefore, a new technique was introduces for drilling at greater depths. To prevent freezing and closing the hole, the borehole was filled with a eco-neutral fluid to prevent bacterial and other contamination.

Schematic drawing of drilling deep Hole #5G (showing 5G-1 and 5G-2). Figure credit: Vesiliev et al. 2011

The possibility of contamination of the lake is the major problem. Besides obvious ecological damage (if microbial life exists in Lake Vostok after such a long isolation it requires strict protection), contamination, if happens, will also bias scientific results. Sediments on the lake’s floor could provide clues to its long-term climate change, while isotopes in its water could help in determining how sub-glacial lakes form.

The drilling technique used by the Russian team include 3 stages
1. An ecologically inert liquid (e.g., polydimethylsiloxane) was injected to the Hole #5G-2 bottom using a special tanker.
2. The hole is deepened down to the ice-water boundary. The access to the lake was completed using the coreless thermal drill system. The drill was cleaned by the produced melt water. This water created a second clean layer separating the bottom of the hole from the drilling fluid. There is 3-4 bars pressure difference between lake water and the hole. Therefore once the tip of the thin pilot drill made contact with the lake surface at 3.769 m it was turned down and pulled up. This will allowed lake water to enter into the hole and to fill up its lower 30–40 meters, pushing drilling fluid up and away from the untouched lake water and thus preventing possible contamination.
3. The third stage could be conducted the next Antarctic season, after checking the frozen sample in the hole.

Possibilities of life

Lake Vostok environment comprises high pressure, low carbon and chemical content, at least 15 million of years isolation, complete darkness and the probable excess of oxygen in water. This doesn’t look like a habitable environment at all. However, after discovering of extremophillies with their ability to live under almost any conditions, there is an optimistic hope that microbial life in the lake may be possible no matter what.

According to Bulat et al (2010) accretion ice was found free of microbial DNA. The only positive results, which passed both the artifacts and contaminant controls criteria checks, include thermophile Hydrogenophilus thermoluteolus. This was first found in accretion ice from 3607 m depth and was confirmed later by examining another ice sample from 3561 m depth.

Because lake water temperature is below freezing point (-2 C, due to pressure), the only niche for thermophiles should be within the deep faults of the bedrock encircling the lake. Combined with geochemical and geophysical considerations, these results nevertheless suggest the presence of a deep biosphere, possibly flourishing nearby active faults of the bedrock, where the temperature could reach up to 50C and in situ hydrogen is probably present.

However, these results highlight another (no less important) problem of searching for life samples with very low levels of microbial biomass. Such samples often show high probability of forward-contamination which results in false positives. Therefore, a special set of indexing contaminant criteria were developed by Bulat et al., (2004) for DNA studies allowing recognition of majority of the findings as possible contaminants. The framework is shown below:

A framework for biological studies adopted for Lake Vostok. Figure credit: Bulat et all (2010)

I think that developing of these techniques is as important as finding life in water of Lake Vostok. This is especially important for future search for life in sub-glacial oceans of Europa and Titan.

Future work

Artist's concept of the cryobot and hydrobot. These robots are in the very initial stages of design and may look very different as the robot design evolves. Credit: Wikipedia

In the 2012–13 season, the Russian team plans 1) to gather water sample from the drill and 2) to send an underwater robot into the lake to collect more water samples and sediments from the bottom. If this happens, that robot would be a predecessor for more ambitions cryorobot proposed for exploration of Jupiter’s moon Europa. The cryorobot for Europa suppose to melt through the ice until it reached the moon’s ocean. Once it reached the water (or if it reaches the water), it would deploy an autonomous underwater hydrorobot which would gather information and send it back to Earth.

References:

“Appeal to the Duma on Lake Vostok, Antarctica”. Antarctic and Southern Ocean Coalition. 14 April 2008. Retrieved 21 February 2011.

“Exploration of Antarctic Subglacial”. National Academy of Sciences. National Research Council. 2007. Retrieved 21 February 2011.

Bulat, S.A., Alekhina, I.A., Blot, M., et al. DNA signature of thermophilic bacteria from the aged accretion ice of Lake Vostok, Antarctica: implications for searching for life in extreme icy environments. Int. J. Astrobiol. 3, 1–12, 2004.

Bulat, S., Alekhina, I., Marie, D., Martins, J., & Petit, J. (2011). Searching for life in extreme environments relevant to Jovian’s Europa: Lessons from subglacial ice studies at Lake Vostok (East Antarctica) Advances in Space Research, 48 (4), 697-701 DOI: 10.1016/j.asr.2010.11.024

DailyMail: http://www.dailymail.co.uk/sciencetech/article-2095193/Lake-Vostok-Russian-scientists-confirm-triumph-drilling-successful-Antarctica.html#ixzz1n2RFqMOf

Dieter Fütterer; Georg Kleinschmidt (2006). Antarctica: contributions to global Earth sciences: proceedings of the IX International Symposium of Antarctic Earth Sciences Potsdam, 2003. Birkhäuser. p. 138. ISBN 9783540306733. Retrieved 21 Feb 2011

Jouzel J, Petit JR, Souchez R, Barkov NI, Lipenkov VY, Raynaud D, Stievenard M, Vassiliev NI, Verbeke V, Vimeux F (1999). “More than 200 meters of lake ice above subglacial Lake Vostok, Antarctica”. Science 286 (5447): 2138–41. doi:10.1126/science.286.5447.2138. PMID 10591641.

Morton, O. “Ice Station Vostok”. Wired. Retrieved 21 Feb 2012.

Oswald, GKA; Robin, G. de Q. (1973). “Lakes beneath the Antarctic Ice Sheet”. Nature 245 (5423): 251–4. doi:10.1038/245251a0.

Vasiliev, N., Talalay, P., & , . (2011). Twenty Years of Drilling the Deepest Hole in Ice Scientific Drilling (11, March 2011) DOI: 10.2204/iodp.sd.11.05.2011

Weiss, K.L. Yung, N. Koemle, S.M. Ko, E. Kaufmann, G. Kargl ; Thermal drill sampling system onboard high-velocity impactors for exploring the subsurface of Europa, Advances in Space Research (18 January 2010)

Here they are:

NASA blogs – daily updates from NASA

sciencemag.org – Science news from Science

BBC Space Science blog from Jonathan Amos

cosmicvariance blog at Discover magazine

KathrynKilian.com – a blog run by a wonderful violin player, Peabody graduate, Kathryn Kilian

artemvovkguitar.com – a blog run by Artem Vovk – a wonderful guitar player, photographer and explorer

scienceblogs.com – a very interesting science blog run by Coturnix

writing.upenn.edu/~afilreis/88/home.html – a web site dedicated to the modern English poetry

OpenCulture – the best free science, cultural and educational media on the web

ericvalli.com – the most beautiful pictures from Eric Valli.

spiekermann.com – the Erik Spiekermann’s (the famous typographer) blog

Erik Spiekerman on DesignMind – legendary type designer Erik Spiekermann talks type with frog, expounding on the beauty – and the difficulty – of designing numbers

The Common Parlance – An erudite discussion about the proper usage of words in the English language. I found it very helpful

cssZenGarden – a beautiful demonstration of what can be accomplished visually through CSS-based design

alistapart.com – the most valuable resource for web designers

I promise to update and expand this list.