Professor Seager's Exoplanet Space Mission Research
Professor Seager's research group works with data from several space telescopes including Kepler, Spitzer, Hubble, and EPOXI. Above the blurring effects of Earth's atmosphere, space telescopes provide excellent observations of exoplanets and their host stars.
Professor Seager's group is also involved in the development of two different MIT space telescopes. TESS (Transiting Exoplanet Survey Satellite led by Dr. George Ricker) will be an all-sky survey for transiting exoplanets, surveying 2 million stars of magnitude 5 through 12. TESS will be proposed to NASA's Explorer opportunity in February 2011. ExoplanetSat will be a triple CubeSat Professor Seager's Space Instrumentation group is developing a small nanosatellite called ExoplanetSat.
Professor Seager’s Space Instrumentation group is developing a prototype nanosatellite capable of monitoring a single, bright, sun-like star for two years. “ExoplanetSat” will develop into a suite of nanosatellites, each focusing on one bright star at a time. The science motivation is to search for transiting exoplanets orbiting the brightest sun-like stars in the sky. Currently, no planned mission has the capability to survey even the nearest stars for an Earth analog. The best way to monitor the brightest sun-like stars (0 < V < 5) for long-duration transiting exoplanets is by a targeted star search; the brightest stars are too widely separated across the sky for a single telescope to continuously monitor. Each ExoplanetSat spacecraft will monitor one star at a time, instead of surveying thousands of stars simultaneously. The detailed properties of each target star are well known in advance.
To take advantage of launch opportunities as a secondary payload, ExoplanetSat is being designed to fit into a Poly-Picosatellite Orbital Depolyer (P-POD). The P-POD is a standardized deployment system developed by California Polytechnic State University. The standardized dimensional (10 cm x 10 cm x 34 cm), mass (~4 kg), structural, electrical, operational, and testing requirements were motivated to enable relatively low-cost CubeSats to be designed, built, and flown by students. Universities have been developing flight-ready CubeSats since before 2003. Many launch opportunities are becoming available, motivating us to package ExoplanetSat into a P-POD.
The present goal is to build and launch an ExoplanetSat prototype that will observe a single target star at a time. After a successful demonstration the goal is to launch a fleet of nanosatellites to search enough stars to find a number of interesting exoplanets.
Conception of the ExoplanetSat prototype with deployed solar panels. Credit: Matt Smith.
NASA's Kepler Space Telescope will answer the ancient question, "How common are other Earths?" Kepler is monitoring 150,000 stars for three and a half years to search for a characteristic drop in brightness indicative of an Earth-sized planet. A huge amount of followup work is needed to confirm planet candidates, that is, light curves consistent with a planet signature, as planets. Most planet candidates will not be confirmed at the 100% level due to astrophysical false positives. Instead Kepler will provide statistical frequency of different kinds of planets. The main goal is to determine the frequency of Earth-size planets in Earth-like orbits about sun-like stars.
Professor Seager's group is involved with the analysis of Kepler data of Jupiter-size and Neptune-size planets, focusing on their radii, albedo constraints from secondary eclipse, statistical properties, and any possible interpretation of physical characteristics. Professor Seager's research group also contributes to the interpretation of rocky planet radii (and masses when available).
Spitzer and Hubble Space Telescopes
NASA's Spitzer Space Telescope and Hubble Space Telescope provide observations of transiting planets, planets that go in front of and behind their star as seen from Earth. Observations of transiting planets exploit separation of photons in time, rather than in space. That is, observations are made in the combined light of the planet-star system. Primary and secondary eclipses enable high-contrast measurements because the precise on/off nature of the transit and secondary eclipse events provide an intrinsic calibration reference. This is one reason why the Hubble Space Telescope and the Spitzer Space Telescope have been so successful in measuring high-contrast transit signals that were not considered in their designs.
Members of Professor Seager's research group analyze data from Spitzer and Hubble and interpret the data to understand the composition and temperature of exoplanet atmospheres.
Artist's rendering of NASA's Spitzer Space Telescope, against an infrared view of the sky. The band of light is the glowing dust emission from the Milky Way galaxy seen at 100 microns (as seen by the IRAS/COBE missions).
Photograph of NASA's Hubble Space Telescope
- Madhusudhan N., and Seager S., 2009, "A Temperature and Abundance Retrieval Method for Exoplanet Atmospheres", ApJ 707, 24
- Madhusudhan N., and Seager S., 2010, "On the Inference of Thermal Inversions in Hot Jupiter Atmospheres", ApJ 725, 261
NASA's EPOXI is a 30 cm telescope now orbiting the sun millions of miles from Earth. EPOXI is a combination of the names for a space mission's two components: the Extrasolar Planet Observations and Characterization (EPOCh), and the flyby of comet Hartley 2, called the Deep Impact Extended Investigation (DIXI). Professor Seager is a member of a team that is using EPOXI to study stars with transiting planets and also to observe Earth from afar. Professor Seager's group is trying to understand what we would learn about Earth as an exoplanet from EPOXI's near infrared spectra of Earth. For a slightly different topic of inversion of EPOXI's Earth orbital light curves to determine Earth's physical characteristics, see the following paper by an EPOXI team member:
Cowan N., and the EPOXI Team, 2009, "Alien Maps of an Ocean-Bearing World", ApJ 700, 915
EPOXI real video of Earth, with the moon transiting. When the images were acquired, the spacecraft was just outside the orbit of the Earth and ahead of Earth by 31 million miles, 1/3 AU, making it as far from Earth as Mercury is from the Sun. Credit: Don Lindler NASA/GSFC. For the video go to http://epoxi.umd.edu/3gallery/vid_Earth-Moon.shtml