I’ve been playing with imaging data recently and found something, probably an asteroid, passing through the Kepler field of view. Its pretty relaxing if you loop it.
I was in a seminar last week where exoplanet science was described as being in the post-Kepler era. This phrase has much merit given how dramatically our understanding of exoplanet populations has changed since Kepler launched. For example in 2007 the state of the art simulations predicted 10-100 Earth mass planets do not form. Kepler data has shown this predicted to be spectacularly wrong. Turns out most planets all into this range.
However, in the talk post-Kepler era was used to describe the era after Kepler stops taking data. Which is now because Kepler is dead, right? Erm, actually no. Kepler is alive and, if not well, doing pretty good. What is true is that Kepler cannot point accurately at its original field, but there are parts of the sky where it can really kick ass – in the ecliptic. Most of the current information is subject to change but our best guess is that we will be able to observe some 10′s of thousands of targets continuously for about 2.5 months. Now here is the real exciting part. Its very possible that we will be able to obtain better than 100 parts per million photometry. That means we could easily detect rocky Earth-sized bodies around Sun-like stars, albeit pretty hot rocks. This capability is unique, nothing else can achieve precision as good as that. This is why I’m super excited by two wheel Kepler. We just need a good name for this refactored mission.
I’m going to try to post on a semi-regular basis about whatever astronomy thing has interested me on a given day. it’s probably be a bit random and not well explained.
Today I was chatting with some by Kepler buddies about a paper by Ofir where they measure the mass of two planets orbiting KOI-1574 using transit timing variations. The part I find interesting is that Ofir finds one of the planets has a density of 0.1 g/cc – much lower than any planet in our own Solar System. We were concerned with the uniqueness of the solution given there are only 4 transits of the planets of each planet in the Kepler data.
Dan Foreman-Mackey has been developing an n-body/transit model code that can be used to used to model systems like KOI-1574. I hope/plan to run an MCMC simulation that should reveal whether the ultra-low density found by Ofir is significant and robust. Not that I’m trying to pick on Ofir, his analysis seems perfectly reasonable to me. It does however provide a convenient example to test the code upon.
We’re back, and by that I mean the US government is back. For the last 16 days I’ve been locked out of my office at NASA Ames. As a contractor I’ve been allowed to work, indeed I’ve had quite a productive few weeks.
The first week of the shutdown the SETI Institute in Mountain View kindly hosted me and provided free coffee! With all the Kepler science office in the same room we were able to chat about a few projects we were all working on and it looks like a few papers that have been a long time coming are nearly finished (Kepler planet catalog papers).
Last week I took the opportunity to visit New York University as a guest of David Hogg. We have a few projects together that have been left on the backburner. Hopefully we/I will get these going this time. One of the more straight forward ideas we have is to measure limb darkening using transit of multi-planet systems.
Anyway, I’m going to try and use this blog as a bit of a research/work journal. It may not work, let’s see.
I’m about to do the press conference to announce this system but I wanted to make the paper available. The paper is available from here.
The press conference should be on NASA TV now.
A recording of the press conference can be found on the NASA UStream page. I’m not sure how long it will last there though.
I did a live interview with the BBC Radio 4 program The World Tonight. That interview can be found via this link - Radio 4 interview.
Recently the International Astronomical Union, IAU, put out a press release where they discussed the selling of planet names. I have some concerns about selling names and such but that is a separate point. What surprised me was that the IAU press release implied that there is an official naming scheme for exoplanets and that they manage it. I recently announced the discovery of three exoplanets and I don’t think I or anyone else on the team asked for permission from anyone to name them Kepler-37b, c and d. As far as I can tell, there is no official naming scheme for an exoplanet. Indeed, there isn’t even an official definition of what an exoplanet is.
Yesterday I spend the afternoon with a film crew from the CBS Sunday Morning News. I got interviewed by Barry Peterson who earlier this year was shot at in Syria. I’m not quite sure what a serious news journalist was doing talking to me but it was fun nevertheless.
They were asking about what it’s like to be a planet hunter. One of the questions they wanted me to answer was ‘What is it like to find a planet? Describe the emotions’. That’s actually a fairly difficult thing to do. There is not really a single moment when you discover something and it isn’t really an individual thing. Many, many people are involved in anything that comes out of a large project like Kepler. However, there were several points in my two recent papers (one a sub-Mercury-sized planet, the other I’m not meant to talk about yet but will come out on Thursday this week) where I got excited. The first was when flipping through the data you find something unusual or extraordinary. The second is when you find that no one else is on to this yet – its not already published and from what you can tell no one else is working on it. This is the spine-tingling moment.
However, after this initial excitement follows months of hard work and strife. The time it takes to go from having an interesting candidate to having a finished paper can be many months. The week or two before a paper is submitted can be intense. Everyone wants the paper out right away. Long hours of writing and editing are generally required. After the paper is submitted the overwhelming emotion is relief. Relief that you can relax for a little while.
By the time the Kepler-37b paper came out I’d been working on the system for well over a year. I was no longer excited by the work because it was old news, not only to me but to everyone around me. I was more excited about moving onto other projects than talking to journalists.
Anyway, the interview with CBS will be shown on CBS Sunday Morning News with Charles Osgood on 21st April. I think the show will be on at 9.30am on the east coast but 6.30am pacific. Apparently, it should be posted online too.
This already a week old now but I thought I’d post some of the press stories. I’ve spent the last year writing a paper that was published in Nature announcing the discovery of an exoplanet smaller than Mercury. This work has taken a long time so it is great that it has finally become public.
We managed to get a lot of press attention. Some of the articles are listed below. Additionally, one of the co-authors of the paper did a great interview on Australian TV.
The information below comes from the NASA public affairs team.
The AP (2/21, Chang) reports scientists using the Kepler telescope data have discovered a planet about the size of the moon, although the exoplanet, called Kepler-37b, “orbits too close to its sun-like star and is too sizzling to support life.” It was discovered by Thomas Barclay of the Ames Research Center and it “took more than a year and an international team to confirm that it was a bona fide planet.” UC Berkeley’s Geoff Marcy said, “This new discovery raises the specter that the universe is jampacked, like jelly beans in a jar, with planets even smaller than Earth.” Alan Boss of the Carnegie Institution for Science, called the discovery a “milestone” towards finding an Earth-like planet.
The Los Angeles Times (2/21, Brown, 692K) reports Barclay said scientists are “breaking new ground” with the discovery, who noted that a total of three planets have been found in the system. While none are similar to Earth, Barclay, according to the article, claimed the “discovery is still ‘really good news’ for the search for habitable worlds…because it demonstrates that the Kepler telescope is sensitive enough to find Earth-sized planets with longer orbits ‘in the not-too distant future.’” Caltech’s John Johnson, who was not part of the study, praised Kepler for making exoplanet discoveries “blasé” with the what it has found.
The Boulder (CO) Daily Camera (2/21, Brennan, 40K) reports on the ties the mission and the discovery has to the region as Barclay said, “This project would not have been possible if not for the exquisite instrument built at Ball.” Meanwhile, Alan Gould, a co-investigator for education and public outreach for the Kepler mission, said, “The significance as far as I’m concerned is that when the mission first started it was hoped that we could find planets smaller than Mars, and we thought it might be able to find planets as small as Mercury. … So, this is momentous in that here is a planet smaller than Mercury, and it is totally due to the incredibly precise light measuring capability of the Kepler instrument.”
According to the Christian Science Monitor (2/21, Spotts, 47K), in another result from this study, “Kepler’s ability to take very precise measurements of the star’s own light helped the team develop a highly accurate estimate of the star’s size and mass.”
SPACE (2/21, Howell) notes “Barclay and his team took great care to confirm the existence of planets around Kepler-37.”
Also covering the story are Bloomberg News (2/21, Lopatto), CBS News (2/21, Harwood) “Space” website, BBC News (2/21, Palmer), Popular Science (2/21, Nosowitz, 1.3M), Wired (2/21, Mann, 798K) “Wired Science” blog, ScienceNOW (2/21, Croswell, 128K), New Scientist (2/21, Aron), Discovery News (2/21, Klotz), another Discovery News (2/21, O’Neill) article, Gizmag (2/21, Szondy), UK’s Daily Mirror (2/21, Rankin, 1.32M),PolicyMic (2/21, Marin), Scientific American (2/21, Matson, 483K), China’s Xinhua (2/21) news agency, Sen(2/21, Black), Universe Today (2/21, Atkinson), The Escapist (2/21, Bolding), Geekosystem (2/21, Chant), andGizmodo (2/21, Diaz).
This is just a short post to mention a very neat paper I have been involved with. The Planet Hunters project gets a group of very proficient citizen scientists to look for planets in data coming from the Kepler spacecraft. They have found 42 new planet candidates in the data. The paper can be found on arXiv and is lead by Yale postdoc Ji Wang.
One of the most exciting thing about this work is that the majority of the candidates have long orbital periods and twenty of these candidates are in or close to the habitable region around their host star. This is astounding because it shows for the first time that planets orbiting the habitable zone are common. Most of their candidates are Neptune-sized planets but if we find large planets we can expect to find small planets. Very exciting!
The blog post feels a little egocentric as I am going to discuss a paper I wrote which has recently been accepted for publication in ApJ. It is a paper which is based on the Kepler data of a star known as TrES-2 and the science we were able to deduce from small brightness variations we measure.
TrES-2 is a star a little smaller than our Sun which falls into the field of view of the Kepler spacecraft. TrES-2 was one three stars in the Kepler field known to host a transiting exoplanet pre-launch (the other two being HAT-P-7 and HAT-P-11). The planet is of similar size to Jupiter and orbits with a period of just under 2.5 days.
One of the keys to understanding exoplanets is understanding the star’s that host the planets. This is because the two most productive techniques for discovering new exoplanets (the Doppler method and the transit method), measure a planet’s mass (for Doppler) and radius (for transit) relative to the stellar mass and radius. Without accurate stellar parameters own knowledge of the planet is severely restricted.
In the case of TrES-2 we were able to determine with very high precision the star’s mass and radius by measuring seismic oscillations on the star’s surface. This technique, known as asteroseismology, is very powerful and is one of the very few ways with which to accurately determine stellar parameters (another being to directly image the star).
With these parameters in hand, the next step was to determine some planet parameters. TrES-2 is fairly bright and has been observed for the entirety of the Kepler mission. As such, the data we have for TrES-2 is some of the most exquisite exoplanet data ever obtained. We were able to observe a number of effects that until recently were thought impossible to see.
Doppler Beaming: The gravitational pull of the planet on the star causes the star to move towards and away from the observer as it orbits and can be seen as a radial velocity shift. This is the principle used to find planets with the Doppler method. It turns out that this effect can also be seen as a variation in the brightness of the star owing to a special relativistic effect known as Doppler beaming. As the star moves toward us, it’s light cone gets beamed very slightly towards us resulting in a slight increase in brightness. As it moves away it gets a little fainter because the light from the star is beamed away from us slightly. The change in brightness induced by transiting planets is very small. For TrES-2 the star only changes in brightness by 3.4 parts per million. Small but (just) detectable.
Ellipsoidal Variations: The gravitational pull of the planet on the star actually deforms the star slightly (remember, the star is a fluid). As the planet orbits the star, we periodically see more then less surface area of the star. The more surface area of the star we see the brighter the star appears to be. The deformation affect may only be to increase to the size of the star along one axis by 10 km or so but again this effect is just detectable. For TrES-2 we detected a modulation in the star’s brightness of 2.7 parts per million.
The reason why the detection of Doppler beaming and ellipsoidal variations is interesting is that both are gravitational effects and hence both depend on the mass of the planet. Therefore, by measuring the amplitude of the effects we directly measure the mass of the planet. This is very exciting as usually determining planet masses is a time consuming and expensive effort involving many nights typically using a very large and expensive telescope. Here we get it for free (almost, I still need to eat).
Phase Variations: Another effect we measured is similar to the different phases of the Moon we see from Earth, as a planet orbits a star we see the day side of the planet followed by the night side. When we see the day side of the planet, we see light. We measure a day and night brightness ratio of 3.4 parts per mission. We are also able to measure an albedo for the planet. TrES-2b was already thought to be the darkest exoplanet. We now report that this planet is about half as bright as we previously thought.