Solar sail technology, still in its early phases of development today, could support missions to the far reaches of the solar system to allow for direct imaging of exoplanets.

Future exoplanet missions: NASA and the world (part 2)

by Philip Horzempa
Monday, October 15, 2012

[Editor’s Note: Part 1, covering several other potential exoplanet missions, was published last week.]

Euclid and WFIRST
There are two dark energy missions that will obtain data on the abundance of exoplanets. The first of these, Euclid, is an ESA mission that has been approved and funded, with a launch targeted for 2020. It will feature a one-meter aperture telescope that will image distant galaxies in the infrared in order to detect the influence of dark energy. As a secondary goal, Euclid will conduct several observing runs looking for the signature of exoplanet microlensing events, making it the first space mission to utilize this approach. Microlensing refers to the fact that as a planet passes in front of a distant star, its gravity will bend that star’s light, as a consequence of Einstein’s general theory of relativity. This bending effect causes a temporary brightening of the distant star, acting as a virtual lens. Given the small mass of planets, the brightening is minimal but detectable. A space telescope that can stare at one patch of the Milky Way for weeks or months is the best way to observe these fleeting and unpredictable events. The importance of microlensing is that it can detect all types of exoplanets at all distances from their parent star. A mission such as Euclid should be able, as a result, to acquire valuable statistics on the architectures of solar systems.

In addition, as Euclid is looking for microlensing events, it will also be able to detect transits like those observed by Kepler. Euclid will observe in the near-infrared, and so is optimized to look for planets around cooler M-class dwarf stars. However, Euclid’s target star field is crowded and the target stars are faint, making transit detection much more difficult than with Kepler. Still, this capability will add to the database of exoplanet abundance.

The Wide-Field Infrared Survey Telescope (WFIRST) is NASA’s version of a microlensing mission. It has languished with almost no funding due to the fiscal effect of the James Webb Space Telescope (JWST). However, a recent development may pull it out of limbo. Earlier this year, the NRO presented NASA with a couple of gifts: two large mirrors polished and qualified for a space mission! Apparently, they were “leftovers” from a cancelled reconnaissance project. Within the past few months, NASA has requested proposals to use these mirrors in a mission. One of the prime candidates would be the WFIRST project. In addition, WFIRST may include an internal coronagraph that would block much of a star’s light and allow study of its surroundings. This, in turn, would enable it to measure the density of dust clouds in other solar systems. Such observations are valuable precursor data for direct-imaging missions, such as New Worlds. However, this mission may not fly until years after the launches of JWST and a formation-flying starshade. Since a precursor must fly before the mission it supports, the exoplanet community is looking for other, near-term, methods to obtain this data.

Small missions
There are a number of smaller exoplanet missions in the pipeline…

Read more: The Space Review: Future exoplanet missions: NASA and the world (part 2).

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