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Tuesday, 29 July 2008

Space-news

Time for news on space, dudes and dudettes! They are 3 and they are quite interesting. The first news is about a discovery of 45 planets in the MILKY WAY with size comparable to that of Earth. If we suppose that only a fraction of all such planets is discovered and that just 1 of those 45 is Earth-like, then again, we'll have a great chance to see an inhabited world. Read the article to find out some cool details, as that they can see the composition of the atmosphere of those planets. Which means that if the world has a space-bound civilization, we could even hope to see glimpses of their activity. Isn't that ultra cool, space fans? Yes, it would be hard, probably we would need a better space-telescope and so on, but still, there is a possibility. And that's not little.
The second article is about GLAST, a new gamma-ray-burst seeker and the third-about the eventual discovery of forming planet. My comments will be below them as usual.

How like Earth are alien planets?

AT LAST we are seeing big rewards in the hunt for “super-Earths” - rocky alien worlds a few times more massive than our own. That was the verdict from a landmark meeting of astronomers last week which saw the unveiling of a huge haul of new exoplanets in our galaxy.

The new discovery of a large number of small planets suggests that they are abundant in our galaxy, and outnumber Jupiter-sized giants by 3 to 1.

This contrasts with the nearly 300 alien planets previously discovered, of which the vast majority are Jupiter-like gas giants. Only a dozen or so are low-mass planets: either Neptune-like ice-worlds or rocky planets like Earth. Now researchers on the High Accuracy Radial Velocity Planet Searcher (HARPS) survey based at the European Southern Observatory in La Silla, Chile, have announced the discovery of 45 more planets in the Milky Way - all of them less than one-tenth of Jupiter’s mass.

They spotted them by recording how each planet’s gravitational tug makes its parent star wobble. According to Cristophe Lovis of the University of Geneva, Switzerland, a member of the HARPS team, these observations suggest that while many of the new worlds are likely to be “hot Neptunes” - planets composed mainly of water with a layer of hydrogen and helium on top - it is probable that some will turn out to be more like rocky super-Earths.

The announcement of this potential haul of super-Earths opens up the exciting prospect that we will be able to glean some detailed information about what these planets are like. For years, astronomers have been waiting for a super-Earth to be found with an orbit that “transits” its parent star: in other words, it passes directly in front of the star as viewed from Earth. This would allow them to deduce many of its characteristics, from its internal structure to the make-up of its atmosphere.

The likelihood of observing such transits is increased when exoplanets have a short orbit around their star. The HARPS planets fit the bill: all orbit in less than 50 days, and some in as little as 10 days. This means that during a relatively short period of observation, the HARPS planets will be much more likely than planets with longer orbits to pass in front of their star.

Now they are hoping the observation of transits (passage of the planet in front of the star as viewed from Earth) will provide us with a robust measure of the planet’s radius, for example, and by combining this with the mass estimate derived from the planet’s gravitational pull on its star it is possible to estimate its density. This in turn can be used to reveal something about the planet’s composition and internal structure.

Most exciting of all, says David Charbonneau of the Harvard Smithsonian Center for Astrophysics, transits allow us to study the atmosphere of a planet. The difference in the intensity of infrared radiation when the planet passes behind its star can be used to determine the temperature of the planet’s atmosphere.

It is also possible to glean information about the composition of the planet’s atmosphere by watching for changes in a star’s spectrum as it filters a fraction of the star’s light during a transit. Such observations of the star HD 189733 have recently revealed the presence of methane and water vapour in the gaseous atmosphere of a transiting Jupiter-size planet.

The dimming in the star’s light will be slight, so such shallow transits are best detected from space rather than with telescopes on the ground, where fluctuations in the Earth’s atmosphere can interfere with the observations.

A few satellites are capable of watching for a transit, among them the Canadian MOST satellite. This is particularly well suited to the task, as its instruments can stare at target stars for long periods of time. source article

Gamma-ray mission may detect dark matter


A computer animation illustrates GLAST's launch and deployment (Courtesy of NASA)
A simulation shows what the ever-changing gamma-ray sky might look like to NASA's GLAST observatory (Courtesy of NASA)
GLAST will scrutinise the sky in poorly-explored regions of the gamma-ray spectrum (Illustration: NASA)
GLAST will scrutinise the sky in poorly-explored regions of the gamma-ray spectrum (Illustration: NASA)

A new NASA satellite with powerful gamma-ray vision is set to launch on 3 June. It will observe the deaths of massive stars, probe the gamma-ray sky for unknown objects, and might even pin down the nature of the mysterious dark matter that pervades the universe.

The $700 million Gamma-ray Large Area Space Telescope (GLAST) is set to launch into low-Earth orbit at 1145 EDT (1645 GMT) from Cape Canaveral, Florida, US. It carries a gamma-ray telescope of unprecedented sensitivity and a monitor that can detect radiation from violent cosmic events called gamma-ray bursts.

The mission will provide the first detailed survey of the sky in a largely unexplored part of the energy spectrum of gamma rays, the highest-energy form of radiation.

The observatory's Large Area Telescope (LAT) is sensitive to gamma rays with energies between 20 mega-electronvolts (MeV) and 300 giga-electrovolts (GeV). The 10 to 100 GeV range is mostly invisible to ground-based telescopes and was poorly sampled by GLAST's predecessor, the Compton Gamma Ray Observatory.

Annihilating WIMPs

The spectrum around 100 GeV offers the possibility of an especially big breakthrough – the chance to identify the nature of dark matter. Dark matter is an invisible substance that outweighs ordinary matter in the universe and has so far only been detected by its gravitational influence on ordinary matter.

The most popular explanation says that dark matter is made of exotic elementary particles that rarely interact with ordinary matter. A zoo of such weakly interacting massive particles (WIMPs) have been proposed, such as neutralinos and axions, but Earth-based experiments have so far failed to confirm their existence.

WIMPs are expected to annihilate and release gamma rays when they hit one another. When GLAST opens its eyes to the sky, it might see bright spots due to clumps of dark matter sprinkled throughout the galaxy. Such clumps are predicted by theory, but whether GLAST will be able to detect them is highly uncertain.

Black hole evaporation

GLAST is bound to provide a wealth of information on some of the universe's most violent events. These gamma-ray bursts can put out more energy in a matter of seconds than the Sun will over its entire lifetime. Most of the bursts are thought to result from the collapse of massive stars and from collisions between neutron stars, while the origins of others are still mysterious.

The GLAST Burst Monitor (GBM) is sensitive enough to detect around 200 gamma-ray bursts each year, about twice the rate seen by NASA's Swift satellite, a gamma-ray burst observatory that launched in 2004. GLAST can see gamma rays across a much wider spectrum of energies than Swift, which will give scientists a more complete view of these events.

There is also an outside chance that GLAST could observe gamma rays from the explosion of microscopic black holes. According to some theories, these tiny primordial black holes would have formed in the violence of the big bang itself. Depending on what mass they were born with, they could be evaporating today in bursts of gamma rays through a process called Hawking radiation. source

My comment: Now, because I work exactly in these field, I can't say I'm not excited about that satellite. It's gonna bring GRB physics to another level, for sure. And maybe it will help us solve the puzzle of GRBs- like the process trough which they emit their massive energy output and the ir origin and so on. God Speed, GLAST!

Has the youngest known planet been spotted?

A team of astronomers says it may have spotted the youngest planet ever found, boasting an age of less than 100,000 years old, and perhaps as young as 1600 years old.

They say it bolsters a controversial theory that planets form very quickly, like stars – but other astronomers say the massive object may not be a planet at all but a 'failed' star, which explains its speedy birth.

Astronomers led by Jane Greaves at the University of St Andrews in Scotland used the Very Large Array of radio telescopes in New Mexico, US, and the MERLIN array at Jodrell Bank in the UK to image the dusty disc around a star called HL Tau. With an estimated age of less than 100,000 years, HL Tau lies about 460 light years away in the constellation Taurus.

Inside the disc, the team found a dense clump of matter at a distance of 65 astronomical units (where 1 AU is the distance between the Sun and Earth) from the star. The clump is about 14 times the mass of Jupiter.

The team reckons that the clump is a planet in its very early years of formation – at no more than 100,000 years old, it is much younger than the previous record holder for the youngest planet, which was less than 10 million years old.

They say the clump probably did not form by the 'core accretion' model favoured by most astronomers, in which planets form slowly, gradually building up mass like dust bunnies.

Instead, it probably formed quickly through a process called gravitational instability, whereby knots of matter in the dusty disc around the star collapse rapidly to form planets. The team says another star called XZ Tau may have kick-started the collapse when it passed near HL Tau as recently as 1600 years ago.

Such a process, which is similar to how stars form, reproduced the observations when team member Ken Rice of the University of Edinburgh in Scotland carried out a computer simulation of the system (watch a video of the simulation).

But the 14-Jupiter-mass object may not be a planet at all. Instead, it may be a brown dwarf – a type of object that is too massive to be a planet but not massive enough to trigger the type of nuclear fusion found in ordinary stars.

If the object grows to be a good-sized brown dwarf, it and its larger stellar neighbour will be more like a binary star system than a planetary system. "I think most astronomers would agree that it is a brown dwarf forming by a 'stellar' process," says Gibor Basri of the University of California, Berkeley, US.

Alternatively, the clump could simply go away. "When astronomers detect blobs of this kind in radio maps of discs, it is difficult determine for certain whether the blob is a forming object, or a transient clump that will dissipate over time," Luhman told New Scientist. source

My comment: That is interesting, but I'm rather skeptical to it, because it's hard to discern whether this is a planet or a brown dwarf or whatever. Not to mention that the gravitational instability is rather cloudy idea and there is still to require from it. But it is interesting to see this developing.

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