NASA will launch a planet-hunting satellite and mount an X-ray astrophysics experiment on the International Space Station in 2017, the space agency announced last week.

Artist's concept of the Transiting Exoplanet Survey Satellite. Credit: MIT
 
The Transiting Exoplanet Survey Satellite, or TESS, will survey whole sky seeking planets circling bright, nearby stars. It follows NASA's Kepler telescope, which is hunting for planets in a narrow field of stars in the constellation of Cygnus.

Scientists expect TESS, which could cost up to $200 million excluding the price of a launcher, will pull back the veil on planets closer to home.

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

The satellite, manufactured by Orbital Sciences Corp., will carry an array of wide-field cameras monitoring stars for dips in brightness caused by planets blotting out a tiny fraction of their light. The craft will launch into a high-altitude elliptical orbit around Earth for a two-year mission.

David Charbonneau, a TESS co-investigator from Harvard University, said the mission could find up to 300 Earth-sized planets in the solar neighborhood. TESS will observe a half-million stars during its mission, according to a presentation by Ricker.

"We're going to be focusing primarily on Earths and super-Earths, covering a wide range of stellar hosts," Ricker said.

The planets identified by TESS will become targets for future more powerful observatories, including ground-based telescopes and the James Webb Space Telescope due for launch in late 2018.

"I think it's fair to say that the targets that we will be able to establish from the TESS mission are ones that will be a resource for humanity for all time," Ricker said. "Once you've carried out this survey and established the nearby transiting systems, you've pretty much defined the ones that are going to be most useful to follow-up missions."

With the help of other telescopes, TESS could enable scientists to study the masses, sizes, densities, orbits and atmospheres of small planets, revealing if the worlds could be habitable.

"The selection of TESS has just accelerated our chances of finding life on another planet within the next decade," said Sara Seager, professor of planetary science and physics at MIT, in a statement.

NASA also picked the Neutron Star Interior Composition Explorer, or NICER, instrument for a $55 million grant.

Artist's concept of the NICER instrument on the International Space Station. Credit: NASA
 
The NICER payload will launch to the International Space Station aboard SpaceX's Dragon spacecraft or Japan's H-2 Transfer Vehicle for mounting on the outpost's truss backbone.

The instrument will measure the variability of cosmic X-ray sources, exploring exotic states of matter within neutron stars, the extremely compact, fast-spinning collapsed remnants of dead stars left after some types of explosive supernovae.

Neutron stars can condense the mass of 1.4 suns into an object the size of a city. The stars can rotate up to hundreds of times per second, emitting X-rays that can be detected by sensors in space.

The NICER instrument will collect spectral data on neutron stars, giving researchers unprecedented insights into the inner workings of the enigmatic objects. Scientists expect to refine models on neutron star structures, composition and dynamics with data from NICER.

NASA made the selections of TESS and NICER in the agency's Explorer program, which has launched more than 90 robotic space missions since 1958.

"The Explorer Program has a long and stellar history of deploying truly innovative missions to study some of the most exciting questions in space science," said John Grunsfeld, NASA's associate administrator for science. "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."