Among the many things that boggle my mind is the fact that we can learn things about the atmosphere of planets that we can’t even see. Take well-studied HD 189733b, a gas giant in close orbit around a K2-class star some 63 light years from us. No one has ever laid eyes on this beast, either in infrared or optical light. But that’s of little moment to the Hubble telescope, among whose tools is NICMOS — the Near Infrared Camera and Multi-Object Spectrometer. It and a lot of ingenuity get results.
A transiting planet like HD 189733b moves behind its parent star every two days or so. When that happens, light from the star itself (the planet now being behind the star) can be compared to the combined light of planet and star when both are facing the Earth. Any emissions from the planet can be examined, a useful window into its atmosphere.
Using such techniques, Mark Swain (Jet Propulsion Laboratory) and team have been able to detect carbon dioxide and carbon monoxide on this world, which had previously yielded methane and water vapor in Hubble and Spitzer Space Telescope observations. HD 189733b is too hot for life, but the find is interesting nonetheless:
“The carbon dioxide is kind of the main focus of the excitement,” says Swain, “because that is a molecule that under the right circumstances could have a connection to biological activity as it does on Earth. The very fact that we’re able to detect it, and estimate its abundance, is significant for the long-term effort of characterizing planets both to find out what they’re made of and to find out if they could be a possible host for life.”
Image: An artist’s impression of the Jupiter-size extrasolar planet, HD 189733b, being eclipsed by its parent star. Astronomers using the Hubble Space Telescope have measured carbon dioxide and carbon monoxide in the planet’s atmosphere. The planet is a “hot Jupiter,” which is so close to its star that it completes an orbit in only 2.2 days. Under the right conditions, on a more Earth-like world, carbon dioxide can indicate the presence of extraterrestrial life. This observation demonstrates that chemical biotracers can be detected by space telescope observations. Credit: Credit: ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI.
Note, too, that this is the first near-infrared emission spectrum ever obtained for an exoplanet. All of this plays nicely into plans for using the James Webb Space Telescope, scheduled for launch in 2013, for Webb astronomers plan to look for biomarkers on distant planets, some perhaps as small as the Earth, using spectroscopic techniques that work best in the near-infrared. Swain also notes that studying molecules in exoplanet atmospheres can help to reveal information about the weather on these worlds, as described in the paper on this work:
In a previous paper, we presented a transmission spectrum of this planet at the terminator, in which methane is seen to be more abundant… in the higher, cooler regions of the terminator region atmosphere. However, it is difficult to compare directly the previous terminator results with our current dayside results because they probe atmospheric regions with significantly different temperatures and altitudes on this highly irradiated planet. The development of sophisticated global circulation and chemistry models could significantly advance the state of the art in this respect.
The paper is Swain et al., “Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b,” accepted by Astrophysical Journal Letters and available online.
Methane and carbon dioxide! How suggestive it is, because the co-existence of both gases in significant amounts indicates a dynamical, unstable atmosphere. Carbon dioxide is almost absent in Jupiter, Saturn, Neptune or Uranus (all carbon is in the form of methane, ethane and so on). Some form of carbon cycle takes place in HD 189733b.
Hi Folks;
One can imagine what the weather might be like within the atmospheres of these hot Jupiters with water vapor, methane, CO2, and the like.
I watched an excellent show about the universe on the National Geographic Channel last Sunday and noted a statement made by the narrator that lightning bolts on Jupiter, or was it Saturn, I am not certain, could be 1,000 times larger than lightning bolts on Earth. I was not certain whether total bolt energy, bolt power, or the length of the lightning bolt was being referred to, but either way, such a lightning bolt in it self staggers the mind, an would also be a beautiful thing to see.
With all of the heat energy within the atmospheres of hot Jupiters, one wonders just how large any lightning bolts within the respective atmospheres could be. Perhaps there would be very little lightning because of a lack of liquid and solid precipiation particulate matter within which electrical charge could build due to the 1,000 K to 2,000 K temperatures of these planets.
Thanks;
Jim
I love it. This is precisely the type of finding that smashes the astronomy skeptics–that is, the people who continually fail to concede that human beings have made a lot of progress in terms of understanding our cosmic habitat. According to their radically skeptical view, astronomers are witch-doctors, make lots of bogus claims, and are really no closer to understanding the cosmos than they were during time of WWI. Many of these skeptics albeit suffer from a combination of frustrated personal lives and/or anti-social personality disorders. Of course, there is much left to understand and I am certainly not espousing a form of scientific triumphalism, but the discovery of molecules in the atmospheres of extrasolar planets is a big deal!
Empirical Constraints on the Oblateness of an Exoplanet
Authors: Joshua A. Carter, Joshua N. Winn
(Submitted on 8 Dec 2009 (v1), last revised 30 Dec 2009 (this version, v2))
Abstract: We show that the gas giant exoplanet HD 189733b is less oblate than Saturn, based on Spitzer Space Telescope photometry of seven transits. The observable manifestations of oblatenesswould have been slight anomalies during the ingress and egress phases, as well as variations in the transit depth due to spin precession.
Our nondetection of these effects gives the first empirical constraints on the shape of an exoplanet. The results are consistent with the theoretical expectation that the planetary rotation period and orbital period are synchronized, in which case the oblateness would be an order of magnitude smaller than our upper limits.
Conversely, if HD 189733b is assumed to be in a synchronous, zero-obliquity state, then the data give an upper bound on the quadrupole moment of the planet (J2 < 0.068 with 95% confidence) that is too weak to constrain the interior structure of the planet.
An Appendix describes a fast algorithm for computing the transit light curve of an oblate planet, which was necessary for our analysis.
Comments: 14 pages, accepted for publication in The Astrophysical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:0912.1594v2 [astro-ph.EP]
Submission history
From: Joshua Carter [view email]
[v1] Tue, 8 Dec 2009 21:06:20 GMT (531kb)
[v2] Wed, 30 Dec 2009 18:39:04 GMT (531kb)
http://arxiv.org/abs/0912.1594