Recently in Science Category

More exoplanet images?

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2008-11-22-bpictoris.jpgNow, this is not 100% confirmed, but it does look like we've got another image of an extrasolar planet: this one (if real) is orbiting the star β Pictoris, a very young star 70 light-years away from us.

The potential discovery comes from a new analysis of images taken in 2003 with ESO's Very Large Telescope. The images were processed to subtract from them the light coming directly from the star, allowing scientists to see objects that are around it; this showed a very distinct point of light very close to the star and in the same plane as the dust ring that surrounds it, but we can't still rule out the possibility that this is a background or foreground object instead of something actually in the neighbourhood of the star.

If this is a real planet, it is closer to its star than the other ones imaged previously, being approximately as far from it as Saturn is from the Sun; it would be a very large planet, though, about eight times as massive as Jupiter.

New observations might prove this object to be a planet (by showing its movement around the star, presumably), so we will definitely hear more about β Pictoris in the future. More details at the ESO press release.

Extrasolar planets imaged directly

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2008-11-14-fomalhaut.jpgThis has been the talk of the Internet today, so I might well write about it as well... for the first time, scientists were able to capture images (in visible light, no less) of not one, but four extrasolar planets orbiting around two separate "normal" stars (we had already seen images of a planet orbiting a brown dwarf star).

First, we have star HR8799, a young star that is a bit larger than our Sun (1.5 times as massive and 5 times as bright) and that lies 130 light years away in the constellation Pegasus. Images taken with the Keck and Gemini North telescopes in Hawaii show three large planets orbiting this star; one is about seven times and other two are 10 times as massive as Jupiter. They orbit the start at distances ranging from 24 to 67 AU (the planetary limits of our own solar system are around 30 AU).

Apart from the historical value of directly imaging these planets, this event is significant for other reasons: this star is very similar to our own, and these large planets are orbiting it at a large distance, leaving space closer to the star for small rocky worlds; in other words, this might be a solar system similar to our own, which is something of a rarity among the hundreds of other solar systems we've already found.

Secondly, we have Fomalhaut, a larger star (2.3 times as massive and 16 times as bright as the Sun) 25 light years away in the constellation Pisces Austrinus, the southern fish. It's been known for a while that this star is surrounded by a large dust disk; in fact, the very sharp inner edge of this disk was a clue that there was a planet there, cleaning out debris just inside the disk. And, indeed, Hubble images do show a bright planet located there, in a very wide orbit around the star. The planet seems to be about twice as massive as Jupiter, and its brightness may indicate it is surrounded by a very large ring system.

The planet orbits the star once every 872 years at a distance that is almost four times the distance from Neptune to our Sun, but since Fomalhaut is brighter than our Sun its appearance would be similar to how the Sun appears when seen from Neptune. Just as is the case with HR 7899, Fomalhaut is a very young star and its solar system is still being formed, which helps in the detection of the planets: they're still hot enough that they radiate brightly in the infrared.

Both stars are visible with the naked eye from a dark sky site, and Fomalhaut should be easily visible even from a urban setting. If you are in Melbourne (or any place at the same latitude), Fomalhaut will be almost directly overhead today soon after sunset — it's bright enough that you can't really miss it. HR 7899 will be a bit harder to find; Pegasus will be visible on the northern sky in the middle of the night, and the Lowell Observatory press release has a diagram that will help you find the right star (it's likely you will need a binocular or small telescope, though).

For more details and images, in addition to the links in the text above, see the (very enthusiastic) Bad Astronomy blog and Centauri Dreams.

AAS meeting

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The American Astronomical Society is now having its annual meeting in Austin, Texas, and as a consequence there is a flood of astronomy news floating around. In fact, there's too much for me to write about, and people that are better (and more knowledgeable) writers than me have being doing a great job of covering the news. So, for lots of information on the meeting, see:

Do black holes exist?

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A while ago (in 2005, I think), I took part in a discussion in a (not astronomy-related) mailing list on the subject of the existence of black holes. The argument of the guy pushing this position was interesting and, for me, very relevant: black holes can't exist because there was no time for them to form.

See, the story is like this: when a super-massive star dies, its core collapses due to gravity and gets progressively smaller very quickly; as it gets smaller, gravity at its surface increases, and so does its escape velocity. When surface gravity increases past a certain point, the escape velocity becomes higher than the speed of light, which means that nothing can escape that body anymore, not even light. Presto, a black hole. After that, the core continues to shrink until it becomes a single point, with infinite density and gravity: a singularity.

However, that's the story as told from the point of view of the shrinking core. As Einstein told us in the theory of general relativity, clocks run slower when in a gravitational field, and the stronger the gravity (or acceleration) the clock is subjected to, the slower it runs. The effect is that, as seen from the outside, the shrinking core actually shrinks progressively more slowly as its surface gravity increases (and, from the point of view of the core, the universe outside moves progressively faster as it - the core - shrinks), and the speed of "shrinkage" tends to zero as the escape velocity approaches the speed of light. Therefore, from the point of view of anyone outside a black hole, the black hole never finishes forming: the escape velocity never actually reaches the speed of light.

It's a good argument, and I couldn't think of a good response to it. It turns out that this is a scientifically interesting problem, and a recent post by Phil Plait, the Bad Astronomer, points to a paper by astronomers from the Case Western Reserve University that argues that not only black holes never finish forming, they can't finish forming because Hawking radiation makes them evaporate before the event horizon forms (from the point of view of an external observer).

Read Phil's article on the subject, as he explains the whole situation much better than I can, and the comments make for excellent reading as well. The original paper, I have to say, was a bit too technical for me...

Recent news

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I haven't been updating this blog much lately... not for the lack of news to comment on, but more for a lack of free time. Now that I'm "back" and, hopefully, with a bit more of free time in the foreseeable future, we'll see more content showing up here. And I'll start with a quick rundown of what's been in the news recently:

Atlantis The shuttle was launched yesterday, finally, and it reached orbit without incident. However, examinations of the thermal protection made in orbit found a 4-inch (10 cm) gap in one of the thermal blankets protecting the underside of the ship. NASA does not seem to be worried about it, as it is not located in any of the areas the suffer most of the heat of re-entry. The shuttle is expected to land on 19 June (Florida time).

Gliese 581c It is not a transiting planet, after all (that is, it never moves between Earth and its star during the orbit). That limits what information can be discovered about this planet in the near future. Still, it looks more and more likely that this planet is not as terrestrial as we'd like it to be; it's more likely that it is more venusian than terrestrial, and the fact that it is tidally locked to its star can't help the weather. Which brings us to...

Gliese 581d This planet received much less attention from the media, but some scientists believe it has a better chance of harbouring life than its more famous brother. Gl581d is significantly farther away from its star (0.25AU, versus 0.073AU for Gl581c), has a longer orbital period (84.4 days) and is more massive (8 Earth-masses). It is also tidally locked to the host star, though. One recent paper argues that a planet of this size is likely to have a dense atmosphere, and certain types of atmosphere would put it safely inside the habitable zone. More relevant still...

Red dwarfs ...stars like Gliese 581 are very, very, very stable after they "mature" (conditions in their vicinity are probably not very friendly during their formative years, though). A planet like Gl581d might stay inside its habitable zone for many billions of years (as opposed to Earth, which will stay habitable for the next billion years or so), which gives it very good chances of eventually developing life. In a "good news, bad news" scenario, though, it is thought that the radiation emitted by the star in its first billion years of life might be strong enough to strip the atmosphere of any planet in the habitable zone without a strong magnetic field, and that any planet in the habitable zone would become tidally locked in its first 500 million years of existence and would lose its magnetic field, thus becoming uninhabitable. We'll have to wait for more advanced instruments to be able to gather more information about what these planets are like today...

New planets There were quite a few; in fact, there were 28 new planets discovered over the last few months. There is a very dense "super-Jupiter" (eight times as massive as Jupiter, but only slightly larger) in a very elliptical orbit around a F-type star (larger and a bit hotter than the Sun) in the constellation Hercules; there was another hot Jupiter in Monoceros, which was interesting mostly because it was the first planet discovered by the European orbiting observatory COROT; another transiting hot Jupiter running a very short (31 hours long) orbit around its host star; a transiting hot Neptune around red dwarf GI-436 (a hot Jupiter is a planet similar to Jupiter — that is, composed mostly of hydrogen — orbiting close to its star; a hot Neptune is similar, but with much more water in its composition); and many more, as reports.

That's it for now. There are certainly many interesting events going on, and the last few months were very exciting in the field of astronomy; let's hope that the trend continues.

Details on Gliese 581 C

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Trying to get away from the media hype surrounding the announcement of the discovery of the new planet orbiting Gliese 581, I learned that there are some important details that are not mentioned in the popular press.

First of all, there's not much certainty about most of the features that would make this planet habitable (at least, habitable to us). What scientist know for sure, at the moment, is the planet's mass, orbital period and distance from its star. The radius of the planet is pretty much a guess based on assumptions about its density, and the idea that it is a rocky/watery planet comes from the same assumptions. The gravity at the surface depends on the same data, of course.

Also, the surface temperature seems to be a very wild guess. After all, the temperature of a planet depends not only on the amount of energy it receives, but also (and mainly) on how much energy it retains. So, the planet's albedo and its atmosphere density and composition play very important roles, and we know nothing about any of these. The temperature range commonly given (0 to 40°C) assumes an albedo similar to Venus's, and I think we all agree that Venus is not quite habitable. If you assume an atmosphere and albedo similar to Earth's, the average temperature is some -17°C (which is still not terrible, and might allow for liquid water in some locations, but is not very inviting; think Hoth).

One extra point is that the planet is so close to the star that it is almost certainly tidally-locked to it; that is, the same side of the planet faces the star at all times (just like the Moon does in relation to the Earth). What impact this would have on the climate of a planet with a dense atmosphere (if this turns out to be the case) is anyone's guess, but the current consensus seems to be that the effect wouldn't be too bad (winds would probably even out the temperatures). It would be an interesting planet to live in, though, with a sun hovering in the same piece of sky all the time (I guess species evolving in this kind of planet would not have a circadian cycle; I wonder what this would do to the inner workings of brains).

None of this makes the discovery any less interesting and important, but it's always a good idea not to get too excited with the information you see in the media. We may get more information (say, about the size and composition of the planet) when it transits in front of the star as seen from here; the next such event is expected to happen next week. As more people look at this system and more information is gathered, we'll certainly get a clearer picture of what life would be like in Gliese 581 C.

Further reading:

Habitable planet discovered

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An Earth-like planet in the "habitable zone" of another star was discovered, according to an announcement earlier today by a team of scientists from the European Southern Observatory. The planet orbits the star Gliese 581, a red dwarf located 20.5 light years away, in the constellation Libra.

The habitable zone of a star is the distance where the temperature in the surface of a planet allows the existence of liquid water. In our solar system, the habitable zone includes Venus, Earth and (barely) Mars. In Gliese 581, this zone is much closer to the star, due to its lower temperature: the planet (called for now Gliese 581 C) is 0.07 AU away from the star, or 1/14th of the distance from Earth to the Sun, and it orbits the star once every 13 days.

At that distance, the estimated surface temperature is between 0 and 40°C; the planet is 5 times as massive as the Earth (but only about 1.5 times larger), which means that its gravity is similarly stronger and it should have a dense atmosphere; there's no word on the possible composition of this atmosphere as yet, though (and, since the planet does not move in front of the star as seen from Earth, determining the composition is a hard problem). With this density, the planet certainly is a rocky world (like Earth), not a gaseous one.

The planet is called Gliese 581 C because it's the third one to be discovered around this star; astronomers already knew of a large, Neptune-like planet orbiting very close to the star (a "hot Jupiter" planet) and another one about eight times as large as Earth orbiting further away, outside the habitable zone.

The Parkes dish looked at this star system, back in 1995, looking for signs of intelligent life, and found nothing; so did the Greenbank Radio Telescope, in the US, with the same result. Still, it is probably going to be at the top of the list of observations when the Allen Telescope Array starts operations later this year.

Update: the original announcement is here

Liquid water on Mars

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Signs of water flow on MarsEarlier this week, NASA announced a press conference for Wednesday morning (US Pacific time; Thursday morning in eastern Australia) with "important news" about Mars. The news are: they have found evidence of liquid water on Mars. The important part is: not in the distant past, but in the last five years.

Two images of the same area of the planet taken by the Mars Global Surveyor in 1999 and 2005 (seen here) show changes that indicate a recent flow of liquid water on the surface; images of a different area show similar activity happening after mid-2002. The supposed flows of water left behind lightly-colored deposits, which are very rare on Mars (disturbances of the soil usually show the darker material that is underneath).

It is presumed that the water flowed from underground deposits, but it's not clear whether the water is permanently liquid (thus providing good conditions for underground habitats for local life-forms) or just becoming liquid for a short period and spurting out of the ground when that happens. When exposed to the thin atmosphere of Mars, liquid water doesn't last very long; it quickly becomes either solid ice (due to the low temperature) or vapour (due to the low pressure).

The Mars Global Surveyor recently stopped sending data and was declared lost, but it clearly brought very important information to Earth; analysis of its images will almost certainly bring more discoveries over the next years. And, of course, the discovery of the presence of liquid water on the planet, even temporarily, brings a boost to the idea of sending people there in the near future.

Supernova caught in the act

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Astronomers reported in Nature that a supernova was caught on camera as it happened for the first time. This was possible because the blast was preceded by a somewhat long gamma ray burst that acted as an "early warning system" of sorts.

Supernova 2006aj (in the constellation Aries) also gives us the first confirmation that supernova blasts do have early signals that can be detected so that the explosion can be predicted and its progress followed; previously, supernovas were only detected visually, and that only became possible several days after the explosion happened.

Dark matter directly "observed"

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NASA has announced yesterday that it has found direct evidence of dark matter in the collision of two large galaxy clusters. This was possible because dark matter does not interact with "normal" matter or with itself in any way other than by gravity, while normal matter is also affected by friction; because of that, "normal" and dark matter were separated during the collision and the gravity-lensing effects of both could be independently measured.

This gives a serious push to the theory that most of the matter of the universe is actually dark matter; the theory explains many observations that would not be compatible with the way we understand gravity to work if only "normal" matter were involved. Other competing theories exist, but none of them explains the observed effects from the galactic collision observed by the Chandra X-ray Observatory. That's not to say that none will show up in the future, but this does add one more hurdle to competing theories.

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