Results from the MESSENGER fly-by
16 Jan at 16:43 by Wilson
Science data is a little slow in coming from this Tuesday’s fly-by of Mercury, but according to NASA everything went as planned and the spacecraft seems to be were it was expected to be. The ground-based antennas are busy handling unexpected problems with Ulysses, another mission exploring that area of the Solar System (it just went over the north pole of the Sun), but we should get more info soon.
Meanwhile, the photo illustrating this article is the first one released by NASA (click on the image to enlarge). It was taken 80 minutes after the closest approach, when MESSENGER was already 27,000km away and looking back. It shows parts of the planet that had never been photographed before (they were not seen by Mariner 10), and that’s just the beginning; we can expect many more pictures over the next few weeks, and we can expect to see most of the features of the planet in colour.
Watching Mercury
9 Jan at 16:16 by Wilson
Now is a good time to look at that small rock sitting very close to our Sun… Mercury is reaching it maximum eastern elongation, which means that it’s about as far away from the Sun (when seen from Earth) as it is going to get this time around. If you have a nice, flat western horizon, look for it soon after the sunset, slightly north of the place where the Sun disappeared. The sky will still be quite bright by the time Mercury sets, but the best day to see it will be on the 21st. For observers in Melbourne, Mercury will set at 21:41 today and 21:42 tomorrow (the Sun sets at 20:45 and 20:44, respectively). For other locations, check this page from the US Naval Observatory.
But, of course, you may prefer to watch it from a better vantage point. If so, now is a very good time: MESSENGER, the first probe to visit that planet since the late 70s, is less than one week away from its first fly-by. The closest approach, at just 200km from the surface, will happen on the 14th, but the cameras will start to take pictures of the planet tomorrow, and some images should be released soon afterwards.
MESSENGER was launched in August 2004 and is in a very complex and long trajectory that will end up with the probe in orbit of the planet… on 18 March 2011. Two more fly-bys happen before then, one in October 2008 and other in September 2009. The reason for this is that it is very hard to send a probe that close to the Sun without having it go into the Sun; it will use its several planetary fly-bys (two of the Earth, two of Venus and three of Mercury) to match its speed to that of Mercury, enabling it to enter the planet’s orbit with relative ease.
Recent news
10 Jun at 15:24 by Wilson
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 exoplanets.org 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
1 May at 16:39 by Wilson
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:
- Gliese 581 C - The Movie: details on assumptions and a simulation of a possible atmosphere
- The Gliese 581 system
- Doubts on Gliese 581 C
Liquid water on Mars
7 Dec at 12:07 by Wilson
Earlier 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.
MRO looks at Opportunity
9 Oct at 10:55 by Wilson
This was posted as one of my “links for the week”, but it’s cool enough to mention on its own: the new Mars Reconnaissance Orbiter is taking very high resolution images of the martian surface since reaching its final orbit; the pictures show a few centimeters per pixel. That’s about as good as the best images of Earth you can see in Google Maps.
And one of the recent images shows rover Opportunity standing by the rim of Victoria crater. The rover is clearly visible, and you can even see the shadow of the camera mast and the tracks it left while getting there. You can see a detail of the image here; click on it to see the full image and the press release.
The ability of seeing the same terrain from two different view points will be very useful to scientists, both in analysing science results and in plotting future movements of the rovers. Come to think of it, it’s quite possible that the MRO will be able to find the ill-fated Beagle, the British lander that was lost in late 2003, which may help pin-point the causes of the loss.
“Xena” has a name
14 Sep at 14:15 by Wilson
2003 UB313, aka Xena, has now an official name given by the IAU: Eris. Its moon, previously known informally as Gabrielle, is now called Dysnomia. Eris is the Greek goddess of discord, while her daughter Dysnomia is related to lawlessness. This follows the general theme for trans-Neptunian objects being named after “not-so-nice” Greek gods.
The IAU announcement is here (PDF document).
Pluto
28 Aug at 17:02 by Wilson
The whole Pluto story has been all over the blogosphere and the regular media, so I didn’t talk about it much. In the end, I liked that the IAU reached a decision (disputed as it may be), even though I actually preferred the option that was announced the week before (12 planets, not 8).
The Australian “Cosmos” magazine has a good editorial online about why Pluto had to go; and, to be honest, I do hope this subject dies quickly and that people get it over with.
No, it’s eight
25 Aug at 9:20 by Wilson
Straight from the “mouth” of the IAU:
RESOLUTION 5A
The IAU therefore resolves that “planets” and other bodies in our Solar
System be defined into three distinct categories in the following way:(1) A “planet”1 is a celestial body that (a) is in
orbit around the Sun, (b) has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a hydrostatic equilibrium
(nearly round) shape, and (c) has cleared the neighbourhood around its
orbit.(2) A “dwarf planet” is a celestial body that (a) is in orbit around
the Sun, (b) has sufficient mass for its self-gravity to overcome rigid
body forces so that it assumes a hydrostatic equilibrium (nearly round)
shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.
1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
Ok, so it’s 12 now?
17 Aug at 14:07 by Wilson
As reported here and in many other places, we will possibly end August with 12 planets in our Solar System: the current set of nine (including Pluto), plus Ceres, 2003UB313 and Charon. The unofficial definition, to be voted next Thursday, is that a planet is any body that orbits a star and is large enough that gravity makes it spherical (or almost spherical).
Ceres is one of the bodies in the asteroid belt, between the orbits of Mars and Jupiter, and it joins the group because it is, indeed, round. It was briefly considered a planet shortly after it was discovered, so it actually regains the status.
2003UB313 is the large trans-Neptunian body discovered in 2003 and recognised last year as being larger than Pluto. Despite a very weird orbit, it actually makes sense to consider it as a planet is Pluto is one.
Now, Charon is a weird one. It is, until now, considered one of the moons of Pluto (and, until recently, the only one); so, it might seem that it does not orbit the Sun, but Pluto. However, Charon is so large compared to Pluto that the center of gravity of the combined system is actually outside Pluto; that is, it’s not so much Charon orbiting Pluto, but both orbiting each other. By the “new rules”, this makes the system a binary planet, and therefore both count as planets.
Interestingly enough, our own Moon is also quite large, in comparison with the moons of other planets. It’s not that large, though, and the centre of gravity of the system is very much inside Earth. But the Moon is getting away from Earth: the average distance increases by some 4cm a year. This means that, in a few million years, the centre of gravity will be outside Earth, and the Moon will be a planet. I really don’t think the IAU rules will still exist (or be relevant) by then, though.
The order of planets our kids will have to learn will, then, be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003UB313 (which will by then have a new name). Now, I don’t know why Sedna and Quaoar were not invited to the party. Maybe that will come later.
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