Archive for the ‘Exoplanets’ Category
Exoclimes.com is a website maintained and animated by professional astrophysicists at the University of Exeter and the University of Oxford. It is a website devoted to discussion around the study of planetary atmospheres outside the Solar System. The website has now reached it’s beta phase. If you haven’t already I would recommend you take a look.
A screenshot from the new website
Astronomers are not able to obtain the transmission spectra of all the Hot Jupiters discovered thus far. With today’s instruments there are about 10 good targets that allow for transmission-based atmospheric detections (Sing et al. 2009b). These stars, which allow for transmission spectroscopy to be done, have the following attributes in common. Either they orbit a bright host star which in turn gives a better signal to noise (S/N), or they orbit a smaller star which leads to a deeper transit, providing a larger planet-to-star contrast. Also if the exoplanet has a large atmosphere (lower surface gravity, higher effective temperature) it is also easier to detect. Of all the Hot Jupiters discovered thus far, two planets stand out as being the easiest to measure, HD209458b and HD189733b. Almost everything known about Hot Jupiters to this date, comes from the study of these two planets.
The escaping atmosphere of HD 209458 b (Credit: Alfred Vidal-Madjar)
HD 209458 b has been the subject of intense study since the first planetary transits were detected (Charbonneau et al. 2000, Henry et al. 2000, Mazeh et al. 2000). It was the first planet to have it’s atmosphere detected using transmission spectroscopy (Charbonneau et al. 2002). What Charbonneau et al. (2002) detected was absorption from sodium which caused a 0.02% deeper light curve relative to simultaneous observations of the transit in adjacent bands. The presence of sodium was later confirmed by Snellen et al. (2008) who used a ground based telescope (Subaru Telescope). Despite this sodium detection, it was not as deep as predicted by a model which assumed a cloudless planetary atmosphere with a solar abundance of sodium. This lead to number of theories such as there being a low primordial abundance of sodium and/or clouds present in the upper atmosphere, to mention a few. Later Rowe et al. (2008) showed that HD 209458 b had a significantly lower albedo than Jupiter using the MOST (Microvariablity and Oscillations of Stars) satellite. This ruled out the presence of bright reflective clouds in the atmosphere. It is now thought that a low sodium abundance is due to condensation (where sodium condenses into sodium sulfide) or ionisation. This is supported by the observation of a sudden abundance change of sodium from the lower atmosphere (where the abundance is about 2 times the solar abundance) to the upper atmosphere (where it is about 0.2 times that of the solar abundance) (Sing et al. 2008). Recent discoveries include the the presence of water in the atmosphere (Beaulieu et al. 2010) and as well as atomic hydrogen, oxygen, and ionized carbon in the upper atmosphere (Koskinen et al. 2010).
The Exoclimes 2012 conference will be held in Aspen, Colorado on January 16-20, 2012. Online registration for the Exoclimes 2012 conference is now available at the Aspen website, by following this link, and click on “Winter applications”. You will need to register and then select “Exoclimes 2012″.
From the exoclimes.org website:
Planetary atmospheres are complex and evolving entities, as mankind is rapidly coming to realise whilst attempting to understand, forecast and mitigate human-induced climate change. In the Solar System, our neighbours Venus and Mars provide striking examples of two endpoints of planetary evolution, runaway greenhouse and loss of atmosphere to space. The variety of extra-solar planets brings a wider angle to the issue: from scorching “hot jupiters” to ocean worlds, exoatmospheres explore many configurations unknown in the Solar System, such as iron clouds, silicate rains, extreme plate tectonics, and steam volcanoes.
Exoplanetary atmospheres have recently become accessible to observations. What observations are possible in the foreseeable future? And how will they constrain the climate on other worlds?
A screenshot from the NASA announcement of Kepler-16 b showing Luke Skywalker on Tatooine
NASA, headed by the Kepler team recently announced the discovery of Kepler-16b, an exoplanet which orbits two binary stars. Something seem oddly familiar? Let’s just say it makes perfect sense to have John Knoll there (visual effects supervisor of Industrial Light & Magic, a division of Lucasfilm Ltd.)
For more news on this matter have a look at this NASA website.
There has recently been a lot of talk in the media about the discovery of new Super-Earths (ESO, BBC). The Kepler team has also announced that they will be revealing new discoveries tomorrow. In this post I thought I might write about the Super-Earths Kepler has found so far.
Super-Earths are a class of exoplanets with masses between 1-10 times the mass of Earth. The study of Super-Earths are of great interest as there is no planet in this mass and size regime in our solar system.
Kepler-10 b is the smallest Super-Earth discovered to date with a Radius of 1.4 Earth radii. It is also the first rocky planet found by the Kepler spacecraft and also the first terrestrial planet found outside our solar system. Here is a video by NASA about this exoplanet:
The Kepler-11 planetary system has 4 Super-Earths (so far) and is the most compact exoplanet system discovered to date. Kepler-11 is a remarkable planetary system whose architecture and dynamics provide clues to its formation. More information on this in the discovery paper.
Kepler-9 d is thought to be a Super-Earth. I say “thought to be” as current spectroscopic observations are still insufficient to establish its mass. The discoverers of the planet led by Torres, G say:
Based on several realistic estimates of this frequency, we conclude with very high confidence that this small signal is due to a super-Earth-size planet (Kepler-9 d) in a multiple system, rather than a false positive.
Worth mentioning here is last weeks news of the discovery of Kepler-19 b. What made this discovery so special wasn’t so much the exoplanet Kepler-19 b but that a companion of this planet, Kepler-19 c was found using transit timing variations (mentioned in my post here). In short, transit timing variations deals with inferring the presence of one or more planets due to timing variations in the expected transit time. For this to be possible, very high quality data is needed, something Kepler provides. Although Kepler-19 is not a Super-Earth it is likely that the transit timing variations technique will discover more Super-Earths in the future.
Artists’s impression of one of more than 50 new exoplanets found by HARPS: the rocky super-Earth HD 85512 b. Credit: ESO
Today 50 new exoplanets where announced by the HARPS team. 16 of them are identified as Super-Earths. One of the Super-Earths is thought to orbit right on the edge of the habitable zone of its star.
ESO Webste:
team has found that about 40% of stars similar to the Sun have at least one planet lighter than Saturn
This is great news and goes to show how fast the field of exoplanet research is moving.
“In the coming ten to twenty years we should have the first list of potentially habitable planets in the Sun’s neighbourhood. Making such a list is essential before future experiments can search for possible spectroscopic signatures of life in the exoplanet atmospheres,” Michel Mayor, discoverer of the first-ever exoplanet around a normal star in 1995.
More info here.
From the ESO website:
On Monday 12 September 2011, astronomers will report significant new results in the field of exoplanets, obtained with the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph on ESO’s 3.6-metre telescope at La Silla Observatory in Chile.
On Monday the 12th at 16:00 CEST an online press conference will take place and a significant announcement will be made. These sorts of announcements are not common so I will admit I am very excited. I only hope that what will be announced is something that will broaden our knowledge about Exoplanets and that it is not just a PR stunt promoting a discovery based upon a mountain of assumptions.
It is hard to say what the announcement will be, but that it might be related to a planet in the habitable zone would be a good guess. Think you know what they will announce? Feel free to present your assumptions in the comment section.
The last month has been especially quiet with regards to exoplanet papers being published. Now though, only days before the Extreme Solar Systems conference in Wyoming, things have really started to pick up. On a daily basis new results are being posted on astro-ph. Here are a few which have caught my interest:
The field of exoplanet research has recently had a big breakthrough. The transit method, which detects exoplanets by measuring the drop in flux from the star which it orbits, is now able to detect multiple planet systems by studying the transit timing variations (delays in expected transit times). This is the first time this has been done. Before only non-transiting multiple planet system where only detected by the radial velocity method.
Photo: David A. Aguilar (CfA)
To read the paper check out: The Kepler-19 System: A Transiting 2.2 R_Earth Planet and a Second Planet Detected via Transit Timing Variations
An artists impression of ultracool dwarfs, and how they might look like to the naked eye, should you ever travel out into space to have a look at them directly. The hotter ultracool dwarf is on the left. Credit: NASA/JPL-Caltech
The direct imaging method, whereby the exoplanet is photographed directly, is one of the most difficult methods for studying exoplanets. To date, less than 30 exoplanets have been studied this way. The type of exoplanets studied using the direct imaging technique are usually big, bright planets with big orbits. Exoplanets too close to the host star simply get lost in the glare of the star, a bit like looking at a firefly really close to the sun on a bright summers day. One way in which we astronomers can learn something about the exoplanet is by performing what is known as photometry. That is, observing how the amount of light from the planet varies over a period of time. This can give ut some hints as to what the upper visible atmosphere is like.
By studying ultracool dwarfs (really cool “small” stars) it will be possible to learn more about the atmospheres of exoplanets. These ultracool dwarfs are similar in temperature to the exoplanets discovered by direct imaging method and also have the advantage of not having a great big blinding star close by. Studying their atmospheres might give us a hint as to what conditions give dusty or clear atmospheres. It is an interesting field of study as it might give us a better understanding of cloud formations in cool atmospheres. Our own solar system show banding and persistent storm systems. How common it is for planets to have these features is something astronomers are trying to figure out.
The Red Spot of Jupiter.
Observational exoplanet astronomer studying the atmospheres of exoplanets. Interested in public outreach and conveying my interest in astronomy to others.
