MIT An artist's conception shows the Transiting Exoplanet Survey Satellite, or TESS, in space. (Planets not to scale.)





NASA has selected two new space missions for launch in 2017: a satellite that can scan the entire sky for exoplanets and a space station experiment that can monitor cosmic X-ray emissions. The Transiting Exoplanet Survey Satellite (TESS) and the Neutron-star Interior Composition Explorer (NICER) won out at the end of a selection process that took more than two years.

"With these missions we will learn about the most extreme states of matter by studying neutron stars, and we will identify many nearby star systems with rocky planets in the habitable zone for further study by telescopes such as the James Webb Space Telescope," John Grunsfeld, NASA's associate administrator for science, said in a statement Friday.

Under the terms of NASA's Explorer Program, the TESS mission will be budgeted at no more than $200 million, and NICER's mission costs will be capped at $55 million. Those price tags exclude the cost of the launch vehicle.

Planet hunter

TESS is designed to follow up on NASA's Kepler mission, which is surveying a patch of sky in the constellations Cygnus and Lyra for extrasolar planets. Like Kepler, TESS would detect other worlds by looking for the faint dips in starlight as they make regular transits across their parent suns. TESS' array of wide-angle cameras would take in much more territory, however.

"TESS will carry out the first space-borne all-sky transit survey, covering 400 times as much sky as any previous mission," principal investigator George Ricker, a research scientist at the Massachusetts Institute of Technology's Kavli Institute for Astrophysics and Space Research, said in a statement. "It will identify thousands of new planets in the solar neighborhood, with a special focus on planets comparable in size to the Earth."

The mission's scientists say it will be possible to study the masses, sizes, densities, orbits and atmospheres of a wide range of planets, including a sampling of the rocky worlds in the habitable zones of nearby planetary systems. "The selection of TESS has just accelerated our chances of finding life on another planet within the next decade," said MIT planetary scientist Sara Seager.

TESS won out over another planet-hunting mission designed to study alien atmospheres, known as the Fast Infrared Exoplanet Spectroscopy Survey Explorer or FINESSE.

NASA An artist's conception shows the boxlike NICER array attached to the International Space Station.

Star watcher

NICER is an instrument that's about the size of a college dorm-room refrigerator, equipped with an array of 56 telescopes that can measure the variability of cosmic X-ray sources — a method known as X-ray timing. It's designed to explore the exotic states of matter within neutron stars and reveal their interior and surface compositions. The device can also monitor the stars' positions as a navigational aid.

"Our technology demonstration will establish the viability of spacecraft navigation using neutron stars, while the same instrument gives scientists an important new tool with which to better understand these stars that can serve as navigation beacons," principal investigator Keith Gendreau of NASA's Goddard Space Flight Center said in a news release.

NICER would be brought to the International Space Station aboard a Japanese HTV robotic transport craft or a SpaceX Dragon cargo capsule, and attached to the station's exterior.

NASA's Explorer Program is designed to provide frequent, low-cost access to space for astrophysics and solar science missions. The program has launched more than 90 missions, starting with Explorer 1 in 1958. The most recent Explorer mission to be launched was the Nuclear Spectroscopic Telescope Array, or NuSTAR. The next one is the Interface Region Imaging Spectrograph, or IRIS, due for launch sometime in the next couple of months.

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Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.