Life After Kepler: Upcoming Exoplanet Missions

Last week I held an interview with Dr. Sara Seager – a lead astronomer who has contributed vastly to the field of exoplanet characterization. The condensed interview may be found here. Toward the end of our interview we had a lengthy conversation regarding the future of exoplanet research. I quickly realized that this subject should be an article in itself.

The following is a list of approved missions that will continue the search for habitable worlds, with input from Dr. Seager about their potential for finding planets that might harbor life.

Transiting Exoplanet Survey Satellite (TESS)

Slated to launch in 2017, TESS will search for exoplanets by looking for faint dips in brightness as the unseen planet passes in front of its host star. With a price tag of $200 million, TESS will be the first space-based mission to scan the entire sky for exoplanets.

While the Kepler space telescope confirmed hundreds of exoplanets (with thousands of candidates yet to be confirmed) it stared 3000-light-years deep into a single patch of sky.  TESS will scan hundreds of thousands of the brightest and closest stars in our galactic neighborhood.

“TESS will find many planets,” explained Seager in our interview. “The ones we’re highlighting it will find are rocky planets transiting small stars.” One of the missions goals is to find earth-like exoplanets in the habitable zone – the band around a star where water can exist in its liquid state.

The team hopes that TESS will find up to 1000 exoplanets in the first two years of searching. This will give astronomers a wealth of new worlds to study in more detail.

While the stars Kepler examined were faint and difficult to study in follow-up observations, the stars TESS will focus on are bright and close to home. These stars will be prime targets for further scrutiny with other space based telescopes.

“We plan to have a pool of planets, maybe a handful of them, that we can follow up with the James Webb Space Telescope … which will look at the atmospheres of those transiting planets, looking for signs of life,” Seager said.

ExoplanetSat

While slightly under the radar, ExoplanetSat will monitor bright stars using nano-satellites. Each nano-satellite will be capable of monitoring a single, bright, sun-like star for two years.

The current design of ExoplanetSat. Image Credit: Pong et al. 2010
The current design of ExoplanetSat. The telescope is approximately the size of a loaf of bread. Image Credit: Pong et al. 2010 (SPIE 7731).

“The way that we describe this mission is not that we will find earth,” Seager said. “But if there is a transiting earth-like planet around a bright sun-like star, we will find it.”

Currently no planned mission has the capability to survey the brightest stars in the sky. TESS will observe stars of magnitude 5 through 12 – the dimmest our eyes can see and fainter.

The brightest stars are too widely spaced for a single telescope to continuously monitor. The best method is to monitor the brightest sun-like stars in a targeted star search instead.

The mission is pretty far along in terms of funding. It has already received a few million dollars and is about one million short of launching the first prototype.

After a successful demonstration the goal is to launch a fleet of nano-satellites to observe enough bright stars to find a number of interesting exoplanets.  One day we may be able to look at a bright star in our night sky and know it has a planet.

Direct Imaging Missions

Disentangling a faint, barely reflective, exoplanet from its overwhelmingly bright host star in a direct image seems nearly impossible. A common analogy is looking for a firefly next to a searchlight across North America. Needless to say, very few exoplanets have been seen directly.

Because of the difficulties NASA is fostering a study and soliciting applications with a single goal in mind: create a mission that will directly image exoplanets under a price cap of one billion dollars.

Seager is working with a team that plans to utilize a star shade – “a specially shaped screen that will fly far from the telescope and block out the light from the star so precisely that we will see any planets like earth.”

The shade isn’t circular but shaped like a flower. Light waves would bend around a circle and create spots brighter than the planets themselves. The flower-like shape avoids this while blocking out the starlight – making a planet that is one ten billionth as bright as its host star visible.

The star shade and the telescope have to be aligned perfectly at 125,000 miles away. Once aligned, the system will observe a distant star, and then move to another distant star and re-align. This is technologically speaking, unchartered territory.

While this mission may not occur in full tomorrow, or even years from tomorrow, astronomers’ synapses are firing. We’re coming up with new techniques that will advance technology and find earth-like worlds.

Etc.

Above is a list of only a handful of future exoplanet missions – all at various stages in their production – with some still on the drawing board and others having received full funding and preparing for launch. With creativity and advancing technology we’ll detect a true-earth analogue in the near future.

 

New Exoplanet-Hunting Mission to launch in 2017

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.

An Orbital Sciences Pegasus XL rocket attached to the fuselage of an L1011 for the launch of IBEX. (Credit: NASA).
An Orbital Sciences Pegasus XL rocket attached to the fuselage of an L1011 for the launch of IBEX. (Credit: NASA).

“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.

Artist's conception of NICER on the exterior of the International Space Station. (Credit: NASA).
Artist’s conception of NICER on the exterior of the International Space Station. (Credit: NASA).

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.

(from left) William Pickering, James Van Allen, and Wernher von Braun hold aloft a mock up of Explorer 1 shortly after launch. (Credit NASA/JPL-Caltech.
(From left) William Pickering, James Van Allen, and Wernher von Braun hold aloft a mock up of Explorer 1 shortly after launch. (Credit NASA/JPL-Caltech).

“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!