New Exoplanet-Hunting Mission To Launch In 2017
TESS will be the first dedicated all-sky exoplanet hunting satellite.
Move over Kepler. NASA has recently green-lighted two new missions as part of its Astrophysics Explorer Program.
These come as the result of four proposals submitted in 2012. The most anticipated and high profile mission is TESS, the Transiting Exoplanet Survey Satellite.
Slated for launch in 2017, TESS will search for exoplanets via the transit method, looking for faint tell-tale dips in brightness as the unseen planet passes in front of its host star. This is the same method currently employed by Kepler, launched in 2009. Unlike Kepler, which stares continuously at a single segment of the sky along the galactic plane in the direction of the constellations Cygnus, Hercules, and Lyra, TESS will be the first dedicated all-sky exoplanet hunting satellite.
The mission will be a partnership of the Space Telescope Science Institute, the MIT Lincoln Laboratory, the NASA Goddard Spaceflight Center, Orbital Sciences Corporation, the Harvard-Smithsonian Center for Astrophysics and the MIT Kavli Institute for Astrophysics and Space Research (MKI).
TESS will launch onboard an Orbital Sciences Pegasus XL rocket released from the fuselage of a Lockheed L-1011 aircraft, the same system that deployed IBEX in 2008 & NuSTAR in 2012. NASA’s Interface Region Imaging Spectrograph (IRIS) will also launch using a Pegasus XL rocket this summer in June.
“TESS will carry out the first space-borne all-sky transit survey, covering 400 times as much sky as any previous mission. It will identify thousands of new planets in the solar neighborhood, with a special focus on planets comparable in size to the Earth,” said George Riker, a senior researcher from MKI.
TESS will utilize four wide angle telescopes to get the job done. The effective size of the detectors onboard is 192 megapixels. TESS is slated for a two year mission. Unlike Kepler, which sits in an Earth-trailing heliocentric orbit, TESS will be in an elliptical path in Low Earth Orbit (LEO).
TESS will examine approximately 2 million stars brighter than 12th magnitude including 1,000 of the nearest red dwarfs. Not only will TESS expand the growing catalog of exoplanets, but it is also expected to find planets with longer orbital periods.
One dilemma with the transit method is that it favors the discovery of planets with short orbital periods, which are much more likely to be seen transiting their host star from a given vantage point in space.
TESS will also serve as a logical progression from Kepler to later proposed exoplanet search platforms. TESS will also discover candidates for further scrutiny by as the James Webb Space Telescope to be launched in 2018 and the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrometer based at La Silla Observatory in Chile.
Also on the board for launch in 2017 is NICER, the Neutron Star Interior Composition Explorer to be placed on the exterior of the International Space Station. NICER will employ an array 56 telescopes which will collect and study X-rays from neutron stars. NICER will specialize in the study of a particular sub-class of neutron star known as millisecond pulsars. The X-ray telescopes are in a configuration utilizing a set of nested glass shells looking like the layers of an onion.
Observing pulsars in the X-ray range of the spectrum will offer scientists tremendous insight into their inner workings and structure. The International Space Station offers a unique vantage point to do this sort of science. Like the Alpha Magnetic Spectrometer (AMS-02), the power requirements of NICER dictate that it cannot be a free-flying satellite. X-Ray astronomy must also be done above the hindering effects of the Earth’s atmosphere.
NICER will be deployed as an exterior payload aboard an ISS ExPRESS Logistics Carrier. These are unpressurized platforms used for experiments that must be directly exposed to space.
Another fascinating project working in tandem with NICER is SEXTANT, the Station Explorer for X-ray Timing And Navigation Technology. This project seeks to test the precision of millisecond pulsars for interplanetary navigation.
“They (pulsars) are extremely reliable celestial clocks and can provide high-precision timing just like the atomic signals supplied through the 26-satellite military operated Global Positioning System (GPS),” said NASA Goddard scientist Zaven Arzoumanian. The chief difficulty with relying on this system for interplanetary journeys is that the signal gets progressively weaker the farther you travel from the Earth.
“Pulsars, on the other hand, are accessible in virtually every conceivable flight regime, from LEO to interplanetary and deepest space,” said NICER/SEXTANT principle investigator Keith Gendreau.
Both NICER and TESS follow the long legacy of NASA’s Astrophysics Explorer Program, which can be traced all the way back to the launch Explorer 1. This was the very first U.S. satellite launched in 1958. Explorer 1 discovered the Van Allen radiation belts surrounding the Earth.
“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,” stated NASA associate administrator for science John Grunsfeld. “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 zones for further study by telescopes such as the James Webb Space Telescope.”
Of course, Grunsfeld is referring to planets orbiting red dwarf stars, which will be targeted by TESS. These are expected have a habitable zone much closer to their primary star than our own Sun. It has even been suggested by MIT scientists that the first exoplanets visited by humans on some far off date might be initially discovered by TESS. The spacecraft may also discover future targets for follow up spectroscopic analysis, the best chance of discovering alien life on an exoplanet in the next 50 years. One can imagine the excitement that a positive detection of a chemical exclusive to life as we know it such as chlorophyll in the spectra of a far of world would generate. More ominously, detection of such synthetic elements as plutonium in the atmosphere of an exoplanet might suggest we found them… but alas, too late.
But on a happier note, it’ll be exciting times for space exploration to see both projects get underway. Perhaps human explorers will indeed one day visit the worlds discovered by TESS… and use navigation techniques pioneered by SEXTANT to do it!
The Hunt for Earth-like Worlds Continues
While Kepler revolutionized exoplanet science by staring at a single patch of sky, its discoveries were often too faint for detailed follow-up. TESS changes that by focusing on the nearest and brightest stars across the entire sky. Over its two-year prime mission, TESS will divide the sky into 26 observing sectors, each covering 24 degrees by 96 degrees. The spacecraft will spend about 27 days on each sector, first surveying the southern hemisphere for a year, then the northern. This strategy ensures that thousands of nearby exoplanets will be found around stars bright enough for precise radial-velocity measurements and, eventually, atmospheric characterization.
The mission’s primary goal is to identify small, rocky planets in the habitable zones of their host stars—worlds where liquid water could exist. TESS is expected to catalog over 1,500 transiting exoplanets, including a few hundred Earth-sized and super-Earth candidates. The brightest of these will become prime targets for the James Webb Space Telescope, which can probe their atmospheres for biosignatures. In this way, TESS serves as a crucial bridge between Kepler’s census of distant worlds and the detailed study of potentially habitable neighbors.
TESS Science Goals:
- Discover transiting exoplanets around bright, nearby stars.
- Measure planet radii and, via follow-up, masses to determine densities.
- Identify the best small planets for atmospheric study with JWST and future observatories.
- Provide a legacy catalog of variable stars and transient events.
Inside TESS: Cameras and Orbit
The heart of TESS is its four wide-field cameras, each with a 24° x 24° field of view. Together, they cover a vertical strip of sky extending from the ecliptic pole to near the ecliptic plane. The cameras use custom-designed lenses and CCD detectors optimized for red-optical wavelengths, where M dwarfs—the most common stars in the galaxy—are brightest. Each camera has a 16.8-megapixel detector, yielding a total of 67.2 megapixels. The optics are kept deliberately simple to minimize cost while achieving precise photometry necessary to detect the tiny dimming caused by an Earth-sized planet crossing a Sun-like star.
TESS will occupy a unique elliptical orbit never before used: a 2:1 lunar resonance orbit. With a period of 13.7 days, the spacecraft’s apogee is always roughly 90 degrees away from the Moon, minimizing gravitational perturbations. This orbit takes TESS from a perigee of about 108,000 km to an apogee of 373,000 km, well outside the Van Allen radiation belts. The high apogee allows long, uninterrupted observations of each sector, while the low perigee permits efficient data downlink. The orbit is stable for decades without the need for propulsion, keeping mission costs low.
NICER: Probing the Densest Matter in the Universe
Neutron stars are the collapsed cores of massive stars that exploded as supernovae. A typical neutron star packs more mass than the Sun into a sphere the size of a city, making it the densest known form of matter. NICER’s primary science goal is to measure the radii of neutron stars to within 5%, a precision that will directly constrain the equation of state of ultra-dense matter. By observing the X-ray emission from hot spots on rotating neutron stars, NICER can use the effects of gravitational light bending and Doppler shifts to infer their sizes. This approach, known as pulse-profile modeling, will for the first time provide reliable mass-radius measurements for several millisecond pulsars.
Millisecond pulsars are neutron stars that spin hundreds of times per second, emitting beams of radiation that sweep past Earth like cosmic lighthouses. NICER’s 56 X-ray concentrators, each with a set of nested grazing-incidence mirrors, will focus X-rays onto silicon drift detectors. The instrument’s high time resolution—better than 100 nanoseconds—allows it to track the pulsar’s rotation with extraordinary accuracy. By timing the arrival of X-ray pulses, NICER will not only constrain neutron star structure but also test general relativity in the strong-gravity regime and search for exotic states of matter such as quark-gluon plasma.
SEXTANT: Navigating by the Stars
Building on NICER’s timing capabilities, the SEXTANT project aims to demonstrate that pulsars can serve as a galactic positioning system. Just as GPS uses atomic clocks on satellites to determine a receiver’s location, SEXTANT will use the ultra-stable rotation of millisecond pulsars as celestial clocks. By measuring the arrival times of pulses from at least three pulsars, a spacecraft can compute its position in the solar system to within a few kilometers, autonomously and without relying on Earth-based tracking. This capability is essential for future crewed missions to Mars and beyond, where communication delays make real-time navigation impractical.
SEXTANT will operate as a technology demonstration using NICER’s X-ray data. During dedicated observation campaigns, it will attempt to determine the ISS’s position using only pulsar timing. Success would validate a key technology for deep-space exploration and could lead to a new era of autonomous navigation for interplanetary probes. Such a system would complement existing methods and reduce the burden on ground stations. The potential for pulsar navigation was first proposed decades ago, but only now do we have the sensitive X-ray detectors needed to make it a reality. As humanity reaches farther into the cosmos, the ability to navigate by the stars—both literally and figuratively—becomes ever more vital. This vision aligns with long-term goals discussed in 100 Year Starship: Crossing the Disciplines.
The Legacy of NASA’s Explorer Program
TESS and NICER are the latest additions to NASA’s long-running Explorer program, which has launched over 90 missions since 1958. Designed to be low-cost and highly focused, Explorer missions tackle well-defined scientific questions with innovative instrumentation. Recent examples include the Swift gamma-ray burst observatory, the WISE infrared surveyor, and the NuSTAR high-energy X-ray telescope. TESS and NICER were selected in 2013 as the next Medium-class Explorer (MIDEX) and Mission of Opportunity, respectively, after a competitive review of proposals. Their combined cost is capped at around $200 million, excluding launch, a fraction of flagship missions.
The Explorer program’s emphasis on rapid development and cutting-edge technology has yielded a remarkable scientific return. TESS and NICER continue that tradition by opening new windows on exoplanets and neutron stars. They also lay the groundwork for future flagship missions: TESS’s all-sky catalog will guide the James Webb Space Telescope’s search for habitable worlds, while NICER’s neutron star measurements will inform ground-based gravitational wave detectors like LIGO. Together, they illustrate how small missions can have a big impact, pushing the boundaries of knowledge and inspiring the next generation of explorers.