SEEJ: Smallsat Exploration of the Exospheres of Nearby Hot Jupiters

Scott Wolk ¹ Jae-Sub Hong ¹ Suzanne Romaine ¹ Almus Kenter ¹ Christopher Moore ¹ Jeremy Drake ¹ Vinay Kashyap ¹ Bradford Wargelin ¹ Martin Elvis ¹ Elaine Winston ¹ Katja Poppenhaeger ² Ignazio Pillitteri ³

¹High Energy, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
²Astrophysics, University of Potsdam, Potsdam, Germany
³Palermo, INAF-Osservatorio Astronomico, Palermo, Sicily, Italy

The first detected exoplanets found were “Hot Jupiters”; these are large Jupiter-like planets in close orbits to their host star. The stars in these so-called “Hot Jupiter systems” can have significant X-ray emission and the X-ray flux likely changes the evolution of the overall star-planetary system in at least two ways:

(1) the intense high energy flux alters the structure of the upper atmosphere of the planet -- in some cases leading to significant mass loss;

(2) the angular momentum and magnetic field of the planet induces even more activity on the star, enhancing its X-rays, which are then subsequently absorbed by the planet.

If the alignment of the systems is appropriate, the planet will transit the host star. The resulting drop in flux from the star allows us to measure the distribution of the low density planetary atmosphere.

We describe a science mission concept for a Smallsat Exploration of the Exospheres of hot Jupiters (SEEJ; pronounced “siege”). SEEJ will monitor the X-ray emission of nearby X-ray bright stars with transiting hot Jupiters in order to measure the lowest density portion of exoplanet atmospheres and the coronae of the exoplanet hosts. SEEJ will use revolutionary Miniature X-ray Optics (MiXO) and CMOS X-ray detectors to obtain good collecting area and high sensitivity in a low mass, small volume and low-cost package. SEEJ will observe scores of transits occurring on select systems to make detailed measurements of the transit depth and shape which can be compared to out-of-transit behavior of the target system. The depth and duration of the of the flux change will allow us to characterize the exospheres of multiple hot Jupiters in a single year. In addition, the long baselines (covering multiple stellar rotation periods) from the transit data will allow us to characterize the temperature, flux and flare rates of the exoplanet hosts at an unprecedented level. This, in turn, will provide valuable constraints for models of atmospheric loss.