Mon, 24 Aug 2009
Planet of the Week: Planet X ?
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Up on arxiv.org today is a paper, "Title: The perihelion precession of Saturn, planet X/Nemesis and MOND", by Lorenzo Iorio.
The perihelion is the point of the planets orbit where it is closest to the Sun. Over the millennia, this point moves, or precesses, under the gravitational pull of other objects. This is a tiny effect, spotted because we have accurate measurements for Saturn thanks to measurements with the Cassini probe. (We have no such measurements further out, for Neptune and Uranus; but we have a more famous case: the Pioneer Anomaly, unexplained changes in the path of the Pioneer probes). Iorio comes up with measurements for a potential planet X to explain this; an Earth-sized planet around 80-150 AU out, up to a Jupiter-sized object at 1000 AU. (1000 times the Earth-Sun distance).I've written before about this: such a planet is remotely feasible to detect by ground-based systems (or perhaps Herschel). It would certainly help explain the architecture of the outer solar system. Perhaps we should start seriously looking for such an object ?
The Brown Dwarf possibility is also interesting; Centauri Dreams has an article on the Wide-field Infrared Survey Explorer (WISE) mission, due for November launch, thats expected to be capable of finding many cold brown dwarfs nearby.
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Thu, 13 Aug 2009
WASP-17b is the first planet to be discovered in a retrograde orbit: it rotates about its star in the opposite direction to the spin of the star. (See the nice BBC News write-up, or the ArXiv preprint for the more technical details).
We think planetary systems are formed from a disk of debris as the star forms, and the disk and star would rotate the same way, so most planets rotate pro-grade, in the same direction of the star. For retrograde motion, it would have to have been hit early-on by some large object (another planetary embryo, for example, being ejected from the stars 'solar system' in the game of cosmic billiards as they coalesce to form planets).
Within our solar system we see retrograde motion in Venus as it spins (on its own axis) in the opposite direction of other planets, but this is the first time we've seen a planet orbit in retrograde. Similarly, Uranus' spin axis is tilted at 89 degrees, but it orbits in a pro-grade manner; its thought that Uranus was hit by a giant object causing its tilt. As we find more exoplanets, the statistics of how many are pro-grade or retrograde will help us learn about the formation of planetary systems.
WASP-17b is a "Hot Jupiter", discovered by the Wide Area Search for Planets (WASP) consortium of UK Universities by Radial velocity methods.
Tue, 18 Nov 2008
Just as life was getting frantically busy, and as catdynamics predicted, Hubble is back open for business with a Supplemental Call for Observing Proposals.
So an idea I bounced off my supervisor has rebounded with a deadline attached. Fun predicted.
Thu, 13 Dec 2007
So, SpaEurope blog reports, with independent confirmation at Dynamics of Cats, that the CoRoT team is ready to do a press release and conference on the 20th December.
Now to go convince my PhD Supervisor to hold off 'til after christmas for the Lit. Review. I suspect he will be devasated to have a hole open in his calendar right in the middle of a week when (undergrad) students are away, and all he has on his Todo list is his own research ...
Wed, 12 Dec 2007
So, the CoRoT team apparently had a meeting in Paris on Monday. I've been waiting with baited breath (and intermittent internet access, for assorted reasons) for the results of a "Press Conference", that according to the blogosphere rumour mill, and a (started by a breathless interim report) was going to rewrite the sciences of exoplanets and stellar seismology. There were rumours of special editions of Nature (or Science, or A & A), Earth-mass planets (possible according to the apparent spec. of CoRoT).
This mattered to me as I'm finishing up a literature review for a PhD and the work is on exoplanets, and depends a lot on stellar variation. CoRoT could rewrite large sections of my conclusions. So, it looks like I finish my review and just have to be patient while they release their results in the proper peer-reviewed manner.
But it would probably be a good idea for the CoRoT team to set up a blog, as Rumour Central, to respond to mentions and rumours about their project that appear on the 'net. Kudos, for example, to Wesley Traub for taking the time to answer my questions aboout Darwin/TPF in this manner.
Sun, 21 Oct 2007
I see from the BBC and /. that ESA has made its choices in Cosmic Vision 2015-2025. It appears that Darwin did not make the cut.
Istead, PLATO and SPICA seem to be holding the banner for exoplanetary exploration.
Can someone closer to the decision-making process comment? What does this mean for NASA's Terrestrial Planet Finder? There were considerations of merging Darwin and TPF; does the project live as TPF, or was the task of imaging an exoplanet left to JWST ?
Sat, 11 Aug 2007
While investigating planet formation (to
).
justifysupportcomplement a PhD proposal on ocean planets), I found this discussion over at physicsforums following a blog entry by Dr Steinn Sigursson. (He uses Planet X in his posts but that is too frequently linked with the dwarf planetXenaEris, and besides, Pluto has been demoted, so its Planet 9 we're looking forThe question is, how was our solar system created ?
Basically, it appears as though there is a planet or substellar companion star out in the Oort cloud. This is not likely to be the Nemesis object of Hut's/Muller's theory, but would have been responsible for the Kuiper belt. Most of the discussion is about brown dwarfs, but following links leads to a paper by Gomes et al., simulating the possibility of outer Neptunes or Jupiters at 4000 AU or 5000 AU. The thread is all about the dynamics of such bodies, but what would they look like?
Now, Hydrogen freezes solid at 14K, Helium is liquid at 4K. So we're talking about a liquid helium ocean on top, with no atmosphere worth speaking of.
But Could it sustain life?
Not as impossible as it seems. Ehrenreich and Cassan point out that an Ice Giant could host a liquid layer underneath an ice shell surface, heated by radiogenic energy, that could last for billions of years before freezing.
So where would it be? This is the time to submit a grant proposal for more envelopes ...
Sun, 29 Jul 2007
Thanks to Centauri Dreams for the pointer to the ESA DARWIN proposal now here (high-resolution version also here). DARWIN is a space mission to detect the presence of life on other planets by spectroscopy: looking for biomarkers such as the presence of Ozone, water and methane together on terrestrial-sized planets. These are groups of gases that collectively would imply the presence of life.
Unfortunately it appears that DARWIN is slipping: its not currently hardware-funded, and has a planned launch-date of 2020, having slipped from 2012. This is when NASAs alternative Terrestrial Planet Finder and Space Interferometry Mission have been defunded indefinitely.
At the same time, the French COROT mission has just announced its first month-long series light-curves. COROT hunts for Earth-sized planets: it's a small space telescope that stares at the same patch of sky for long periods, looking for changes in the amount of light from stars that indicate a planet passing in front of a star. It has been much more successful than expected, having already announced its first exoplanet detection in April. NASA is also launching a similar mission, Kepler, in 2008.
So we face the prospect that any day now we may know of Earth-sized planets in a Habitable zone, and yet be over a decade from determining if they could contain life.
So do we have any other tricks up our sleeves? Other possibilities include the James Webb Space Telescope, the successor to the Hubble. With a launch planned in 2013, it would be able to determine some atmospheric features found in COROT detections, but would be too expensive to do the planet-hunting Darwin could do. Perhaps this could be imroved with occulters such as UMBRAS (thanks to enzo). Other novel detection missions include the Voyager Interstellar Mission (via), reusing exisiting 'end-of-life' spacecraft as telescopes.
And finally, could ground-based telescopes do it? tests have just started on a new 10M telescope in the Canaries that could help; in terms of larger scopes, colleagues of mine in NUI Galway have been collaborating on the design of Euro50, a proposed 50M telescope. Together with new techniques such as spectral deconvolution (via) may help.
Tue, 24 Jul 2007
From Enhanced atmospheric loss on protoplanets at the giant impact phase in the presence of oceans, Genda et. al, Nature, 2005.
Tue, 29 May 2007
Rare Earth proposes that Complex life is rare in the Universe. Paradoxically it first points out how abundant simple life is on Earth, in deep ocean vents, several km below the Earths surface, geysers: places that a few decades ago we would have considered completely inhospitable turn out to host life. But, they argue, complex animal and plant life (eucaryotic life) takes special conditions that they argue are probably unique.
This book is an excellent starting location for someone learning about the state of the art in astrobiology. It summarises well the myriad sciences involved in why life exists on Earth, from astrophysics (is our place in the Galaxy special), planetary development (why only Earth appears to have life in our Solar system), through aspects of geology and biology that we begin to understand. I well recommend this book to anyone interested in these fields. It also has a sufficient reference section to continue the discussion.
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Sun, 27 May 2007
Thanks to Apparent Brightness for this snippet:
Fri, 25 May 2007
Outflows have been discovered from a Brown Dwarf star, 2MASS1207-3932, the lightest yet.
Found by Emma Whelan and Tom Ray of DIAS and others , using the ESO's Very Large Telescope (VLT), this is the first time that Jets have been seen from an astronomical object as small as this.
The Brown Dwarf is 2MASS1207-3932, a 24-Jupiter mass 'near star'. Jets of material are a common feature in astrophysics, seen from Galaxies and young stars, but this is the first time they have been seen in something this small. It opens the possibility of similar outflows from smaller objects, such as giant planets.
The brown dwarf 2MASS1207-3932 is full of surprises. Its companion, a 5 Jupiter-mass giant, was the first confirmed exoplanet for which astronomers could obtain an image, thereby opening a new field of research - the direct detection of alien worlds. It was then later found that the brown dwarf has a disc surrounding it, not unlike very young stars.
Sun, 06 May 2007
According to The Irish Times Weekend Supplement, todays recommended viewing includes We Love the Sky at Night, BBC1, 4.45pm
Fri, 04 May 2007
Greg Laughlin from UCO Lick pointed out that there is a transit possible of Gliese 581c on May7. Looking at the ephemeris, its at 17:13 UT, though: not very good for those of us in Ireland. Yesterdays Nature (subscription required) shows that someone is going one better:
They reckon on 50/1 against a transit, on geometrical grounds. Good luck to them though.
The point of all of this is that the current planetary detections of Gliese 581b and 581c are Doppler radial velocity measurements. While they tell us the period, they only give us a lower bound on the mass : 581c is at least 5 Earth masses, but could be much more (its M Sin(i), where i is the inclination relative to us is unknown). We also don't know the radius of the planet : the figure quoted in the news articles to date is just a guess based on 5 Earth masses and current theory. A transit measurement, where the planet passes in front of the star, could answer these questions.
But it occurs to be we could get numbers tonight: there is a transit (alignment) of Gliese 581b tonight at 22:40 UT. Much more favourable to those of us in Europe.
A transit of GL 581b, the big neighbour of Gl 581c, would tell is that a transit of 581c is likely, and would give us an accurate mass for 581b, and from this, a measure of the inclination. So we could also calculate the mass of 581b.
Unfortunately I don't have a photometer or CCD. Anyone else up for it?
Clear Skies over Ireland forecast , too ...
Sat, 28 Apr 2007
Now that the weekend is here, I've been catching up on the news of this weeks big astronomy announcement: the discovery of a possible "Super-Earth" exo-planet, Gliese 581 c. This is the first exoplanet likely to be within the so-called "Habitable zone" around its star, where life as we know it could be possible. Unfortunately the Irish Times "World Apart" weekend supplement article has been quite disappointing.
Like Greg Laughlin at UCO Lick I get depressed when people give misleading information . It includes a very misleading "Artists impression" picture, simultaneously showing details we don't know and being incorrect about the few things we do know.
Its easy to get annoyed at the concentration of facts that are guesswork or probably wrong in this article. Gl 581c is not 5 Earth masses: thats its minimum mass: due to radial velocity measurements, we can only measure M sin(i), where i is the inclination, currently unknown. It could easily be far more, and hence all predictions of what the planet is like become moot.
Similarly, the radius is not necessarily 1.5 times Earths: thats a prediction, based on the mass, and current theories. Unfortunately, there is no mention that current theories of planetary size are coming under scrutiny as they fail to match other recent exoplanet discoveries. This makes other speculation about the planet such as the gravity on the surface quite misleading.
The BBC News summary is much better: it refers to the radius as "the radius should be", rather than "is". But it too includes the incorrect picture. While its article is couched in more conservative language, it doesn't explain what facts it quotes are speculation and why they may be wrong.
None of the media reports I have yet seen mention current missions, such as COROT, which is the most likely to find Earth-sized planets in the near future (launched late last year, it is due to finish its first observing run in April. Results awaited with anticipation). They also ignore Darwin and the The Terrestrial Planet Finder, the most likely missions to discover life on other planets, but currently sitting in funding limbo.
Concentration on purely the known facts would of course make the news reports short and boring. Instead they should emphasise more of the work of the scientists involved: we teach science as a set of cut-and-dried facts that often bore school students and drive them away.
Instead, when faced as the cutting edge of an important discovery like this, we could show how an amateur could be partially credited with getting this result; with the fact that, since the planet has a short "year" astronomers are already lining up to investigate transit measurements of it on May 7 and that with a magnitude of 10.6 (only 20 light years from Earth, after all) its within range of amateur astronomers to observe and determine its true size and details. How about getting people excited to get involved themselves?
Thu, 19 Apr 2007
As a followup to the talk given at Galway Astrofest 2007 by Dr. Aaron Golden on work done by the Cool Stars research Group here at NUIG, the detail of this work were announced this week at the RAS National Astronomy Meeting 2007. Other press releases can be found at Spaceflight Now, and NRAO, though the best summary is probably at the NUIG Webpage (Thanks to Ronan Newman for the links). Kudos to all involved: Gregg and Stephen are currently writing up their PhDs and should have an interesting dissertions from this.
Basically, they discovered that some Brown Dwarfs can act as Pulsars, blasting out huge amounts of radio-wave energy. Brown Dwarfs are objects between 'Planet' and 'Star' in mass terms, often thought of as boring failed stars, not large enough to ignite into fusion. They were thought by most to be highly boring : this discovery was completely unexpected.
As the group in Galway has a lot of pulsar experience, they were well set to explain this. It looks as though this phenomena is due to a 'coherent maser' : an effect seen in large planets such as Jupiter, where the magnetic field spins up electrons from a solar wind. Certainly, it makes Brown Dwarfs, undiscovered until 1994 but thought to be widespread across the universe, more interesting things to look at.
Sat, 17 Mar 2007
Looking for Earths: The Race to Find New Solar Systems is an excellent introduction book, as a scientific story of exploration and summary of the science of planetary discovery.
Alan Boss is a planetary scientist and adviser to NASA on the search for extrasolar planets. He has had a front-row seat in the revolution over the last two decades that has led to the discovery planets outside our Solar system for the first time, leading to 215 known planets at last counting.
The book is written in an first-person style that reflects the race to discover the first exoplanets in the 1990s. He describes historical searches for planets in the early 20th Century: the hunt for evidence of planets around Barnards Stara and the meticulous work over decades of Peter Van de Kamp, a good summary of the challenges in proving the case for planets in Astronomy, and explains the techniques used to determine other planets. The heartbreaking difficulties of proving the discovery are well expressed, as well as documenting the leaders of the field at the time. Along the way, he describes the discovery of the first Brown Dwarfs, the border cases between Stars and Planets, and the bureaucratic and other challenges involved in setting up large observatories such as the Keck interferometers capable of doing this work.
This is ironic, as the first discoveries were actually made by ground-based observatories. Boss describes the race between the main teams, Geoffrey Marcy and Paul Butler of Lick observatory. The race was finally won by Michel Mayor and Didier Queloz of Geneva Observatory, who discovered the first extrasolar planet around a sun-like star, 51 Pegasi, by looking at radial velocity measurements of nearby stars. This turned out to be a close race, as the planet they had found had a short period of 4.23 days, implying the planet was what we now call a "hot Jupiter", orbiting very close into the Sun. Most teams had been looking for copies of our Solar system, looking for large planets such as Jupiter with orbits of around a decade, and had hence not started to analyse the data they had in hand, expecting to need years of measurements: examining the data showed that, had they analysed data in hand, they could have won.
Looking for Earths does a good job of explaining the field of exoplanet research as it was evolving over Boss's careeer and particularly 1995-2005, with theoretical and computer models evolving as data arrived with new puzzles. In some places, the need to give a clear explanation of a topic such as the formation of planets from solar disks slows the pace of the biography, but the book does an excellent job of describing both the science and the life lived by those doing the work. Few books I've read have offered such a good summary of the field to date, along with a good bibliography and I would heartily recommend it both as an introduction to the field and as a model for science writing.
Wed, 21 Feb 2007
After singing the first verse for many years to my kids at night, I chanced upon the full words to this lullaby fairly recently, in an old book on Astronomy for children, Among the Stars by Agnes Giberne, 1885.
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Mon, 12 Feb 2007
Now the proud owner of a Meade 200mm SCT, with accessories. Pics, and the story behind it, here.
Unfortunately, the accessories didn't include a mount. So now, I'm in the market for a mount, looking for a Celestron ADM or equivalent at the moment. Any recommendations or reviews, anyone?
Of course, cloudy skies are forecast for Galway for the foreseeable future.
Update: Celestron ADM mount on order from Telescope-Service, Germany. Expect clear skies for the next few days until it arrives.
Sun, 11 Feb 2007
I went to the Astronomy Festival on Jan 27 organised by Galway Astronomy Club. Worth seeing; it attracted about 100 people (the Hotel conference room was full); successful for a town like Galway, so frequently covered in Cloud.
Dr. Lucie Green save a good talk on Solar Physics, describing the different methods we now have of exploring the Suns behaviour, Flares, Sunspots, etc. and the different missions such as SOHO and the new STEREO mission to observe the Sun.
Prof. Chris Dainty gave a clear presentation describing the state of the Art in Adaptive Optics, and work his group has been doing, both in Astronomy and pushing AO into other fields, such as opthalmology (treating the eye as the obstacle and observing the retina behind) and productising A.O. for 'non-professional' use. He hopes in the near future to be able to provide Adaptive Optics to Amateurs (price range around Eur 5000, status: not ready yet, the first units would be for 'University Dept' observatories, costing 20-30k, in the next year or two).
Of particular interest were one by Prof. Dick Butler, head of the Chemistry dept. here in NUIG; it was on Organic Chemistry and meteorites. He is a long-time amateur astronomer but professional chemist; he was particularly interested in the organic chemistry of the Murchison meteorite. After pointing out the out the false alarm of ALH 84001, he gave a convincing presentation of the extra-terrestrial origin of complex organic compounds, including amino acids, etc. in the Murchison meteorite. In particular he disputed claims that the meteorite was contaminated, pointing to the Deuterium enrichment of the compounds within; as the C-D bond is stronger that C-H, Carbon-Hydrogen compounds are more likely to be broken up by extraterrestrial radiation that their deuterium variants, leading to deuterium enrichment over terrestrial equivalents. Later he gave a nice summary of conditions on Saturn's moon Titan, pointing to its rich supply of organic compounds, showing that when hit by meteorites, lakes of water would be possible for several hundred years at a time, as the impact craters cooled, and called Titan a utopia for organic chemistry exploration.
This seems to make the idea of panspermia: life originating off-Earth more plausible. For a while now I've had a book (found in the Bargain bin somewhere) by Fred Hoyle and Chandra Wickramasinghe, From Grains to Bacteria, a collection of papers documenting their belief that they've discovered bacteria in free space via spectroscopy. I must admit my spectroscopy is not up to challenging them; time to dig deeper and fish it out.
Dr. Aaron Golden gave a very interesting talk on Brown Dwarfs: Planets or Pulsars that he and his students have been doing. Basically it turns out that while Brown Dwarfs have long been seen as the 'runt' of the Stellar world, stars that didn't make it, some of them it seems are Pulsars. (He's invented the acronym SPUDs: Sporadically Pulsating Ultracool Dwarfs, for them; maybe it'll help people remember that Pulars were originally discovered by an Irishwoman, too).
This was first seen by Aarons' Postgrads Greg Hallinan and Steve Bourke - (see the papers). Kinda interesting as Aaron studied under Dr. Andy Shearer in NUIG working on Pulsars, so knew a bit about them, and had seen behaviour like this before, with a bit of a clue what might be causing it. It was wierd going to this talk; Andy hired me to work in ICHEC, and we have an office in NUIG; Greg and Steve work down the hall, and indeed, I see them occasionally working on our computers; but didn't know what they'd been working on until now.
So, it appears that these Brown Dwarfs (they've seen Pulsar behaviour in several) have Starspots (details here and here; some hot-off-the-press stuff: rumour has it he was checking the results of observations from the night before to ensure they didn't disprove what he was about to say). Aaron was pointing out the coherent maser behaviour was similar to that seen at Jupiter, leading to its strong radio emissions. I didn't get to talk to him about it in detail, but the idea of an Object with both sunspots and clouds sounds fairly exotic and interesting.
Beyond that, the Festival was a good opportunity to see what Irish Amateur Astronomers have been doing, and meet some interesting people. Kudos to all those who organised it.