→ Widely unknown Exoplanet Astronomer

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.

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).

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 – The smallest Super-Earth

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:

Kepler-11 – A planetary system with multiple Super-Earths

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 – Thought to be a Super-Earth

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.

Secret companion found via Transit Timing Variations

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.

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.

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.

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

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.

The ultracool approach

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.

Credit: Swinburne Astronomy Productions

Like wildfire, the news about the diamond planet spreads across the web to the extent where the daily tabloid The Mirror decides to write about it. And why shouldn’t they? It is exciting, right? The only problem I see is that the oversimplified summary of the published result is treated as a certainty. Although this is a great theory, which causes a lot of interest around astronomy and exoplanets, it should be treated with a bit of caution before we start imagining a sparkling diamond planet about the weight of a Jupiter floating around in space. Now is the time for astronomers to debate and discuss the results. Then who knows, once the assumptions concerning the discovery have been constrained we might in a few years time know what part of this announcement was correct or not.  The way the news have presented the announcement makes it seem as if this announcement is the discovery of a diamond planet, which it is not.

Feel free to comment below.

Credit: NASA

Exomoons are moons expected to orbit exoplanets. Although no exomoon discovery has been published to date, there is no doubt that we will find them.

In a recent paper by Simon et. al titeled: Signals of exomoons in averaged light curves of exoplanets they set out to suggest a new method for discovering these exomoons, the so called “Scatter Peak” method. The idea is to study the local scatter in a number folded lightcurves (ideally a 100 or more). It is thought to that this method will allow the discovery of moons around planets with a period of 10-20 days assuming the observations are done during 3 to 5 year long observing campaigns using space observatories.

I find the Scatter Peak method for detecting exomoons very promising provided the three conditions imposed by the authors of the paper are met:

1. The stacking of the individual lightcurves has to be extremely accurate  so that the transit times coincide.
2. The transit observation has to have a continuum (flat part of the lightcurve) which is at least as long as the transit duration itself.
3. The trend filtering must be done so that small deviations immediately before and after the transit of the exoplanet remain unaffected.

A great resource to find out more about exomoons is the recently submitted PhD thesis of David Kipping titled:

“The Transits of Extrasolar Planets with Moons”

Credit: NASA

The Exoplanet group lead by Dr. David Sing at the University of Exeter has been awarded nearly 200 hours of telescope time at the Hubble Space Telescope. As a PhD student of his this means a busy time ahead of me.  The awarded telescope time will be used to study the atmospheres of Exoplanets.

Dr. David Sing:

“This is one of the biggest exoplanet research programmes ever using the Hubble Space Telescope. It is a major coup for the University of Exeter to have secured such a significant amount of time on the world’s best telescope”.

“Astronomers have now detected hundreds of exoplanets and we now know that some of these planets have extreme environments, unlike anything in our own solar system. Everything we have discovered so far about these planets has been puzzling so I am expecting the unexpected.”

Further reading: BBC News, University of Exeter and University of Arizona

In short a paper based on loads of assumtions and in my opinion, not contributing a whole lot of science to the field of exoplanets. I am sure that this is something that media will like to mention but for me it is nothing special. I find the conclusion of the paper summarizes my opinion:

“assuming models for rocky planets with H2O/CO2/N2 atmospheres”

further followed by

“We find that HD 85512 b could be potentially habitable if the planet exhibits more than 50% cloud coverage”

and

“If clouds were increasing the albedo of HD 85512 b, its surface could remain cool enough to allow for liquid water if present”

What do you think of the paper? Commenting is available below

New Kepler data from quater three is scheduled to be released on 23rd of September. This will be the data collected from September to December 2009.

The data will be available at:

http://archive.stsci.edu/kepler

Credit: STSCI