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Kepler Space Telescope: Exoplanet Hunter

by Elizabeth Howell, SPACE.com Contributor   |   March 04, 2014 02:05am ET

NASA’s Kepler Space Telescope is an observatory in space dedicated to finding planets outside our solar system, particularly alien planets that are around the same size as Earth in the “habitable” regions of their parent star.

Since the launch of the observatory in 2009, astronomers have discovered hundreds of extra-solar planets, or exoplanets, through this telescope alone. Most of them are planets that are ranging between the size of Earth and Neptune (which itself is four times the size of Earth).

In the early years of exoplanet hunting, astronomers were best able to find huge gas giants — Jupiter’s size and larger — that were lurking close to their parent star. The addition of Kepler (as well as more sophisticated planet-hunting from the ground) means that more “super-Earths” have been found, or planets that are just slightly larger than Earth but have a rocky surface.

Explanation of new exoplanets found by Kepler Space Telescope.

A powerful new technique for hunting alien planets yields a major new crop of new worlds. [See how Kepler made the planet discoveries in this Space.com infographic]
Credit: By Karl Tate, Infographics Artist

Primary mission

The $600-million Kepler was originally launched in 2009 with the expectation that it would last a year. Gazing at a fixed spot in the constellation Cygnus, the telescope continually monitored 100,000 main-sequence stars for planets. The telescope detected these exoplanets through watching for stars dimming as planets pass in front of them.

Because star dimming can also take place through other means (for example, another star slightly grazing the surface), in the early days these planets were confirmed through other telescopes, generally by measuring the gravitational “wobble” the planet has on the star.

In February 2014, however, astronomers pioneered a new technique called “verification by multiplicity,” which works in multiple-planet systems. A star with multiple planets around it is gravitationally stable, according to the theory, while a star that is part of a close-knit system of stars would have a more unstable system because of each star’s massive gravity. Through this technique, the team unveiled 715 confirmed planets in one release, which was then the largest single announcement. [Gallery: A World of Kepler Planets]

Kepler was approved far beyond its original mission length and was still operating well until May 2013, when a second of its four reaction wheels or gyroscopes failed. The telescope needs at least three of these devices to stay pointed in the right direction. At the time, NASA said the telescope was still in perfect health otherwise, and investigated alternate mission ideas for the hardware.

New mission

Within a few months, the agency came up with a mission that it dubbed “K2.” The mission would essentially use the sun’s solar wind to stabilize the telescope’s pointing for several months at a time. Then, about four times a year, the telescope would move to a different field of view when the sun got too close to its sensors.

The mission is under a senior-level review, with approval or disapproval expected later in 2014. Kepler is still working well, minus the loss of two of its 21 “science modules” used for observations. One died early in Kepler’s mission, and the other one failed during a K2 proof of concept test.

Kepler's Potential K2 Mission Explained

This conception illustration depicts how solar pressure can be used to balance NASA’s Kepler spacecraft, keeping the telescope stable enough to continue searching for transiting planets around distant stars.
Credit: NASA Ames/W Stenzel

Major discoveries

Kepler’s major achievement is showing the sheer variety of planetary systems that are available. Planet systems can exist in compact arrangements within the confines of the equivalent of Mercury’s orbit. They can orbit around two stars, much like Tatooine in the Star Wars universe. And in an exciting find for those seeking life beyond Earth, the telescope has revealed that small, rocky planets similar to Earth are more common than larger gas giants such as Jupiter.

Kepler’s largest discovery in sheer volume occurred in February 2014, whenastronomers unveiled 715 new worlds confirmed in one go. The single release of information nearly doubled the number of known planets to that point to almost 1,700. Astronomers noted this find, using the verification by multiplicity technique, came out of the first two years of Kepler data. Two years of data remain to be studied, and investigators expect hundreds more could come out of examining that information.

Kepler was the first telescope to find a planet approximately the size of Earth in the habitable region of a star. Dubbed Kepler-69c, the exoplanet is about 2,700 light-years away and has a diameter about 1.5 times that of Earth.

The telescope also has the capability to find planets that are much smaller than Earth, such as Kepler-37b. The planet is considered to be close to Mercury’s size and is likely rocky and airless, much like the planet in our own solar system.

Other weird worlds discovered by the telescope include Kepler-62e and Kepler-62f, two water worlds that likely have a global ocean — as opposed to Earth, which has a significant fraction of dry land. The planets are about 1,200 light-years away in the constellation Lyra and are close to the size of Earth.


Europe to build planet-hunting observatory

Posted: February 22, 2014

The European Space Agency has selected an observatory for launch in the next decade to stare at up to a million nearby stars for signs of habitable worlds and probe their size, mass and composition.

Artist’s concept of PLATO. Photo credit: Thales Alenia Space

The PLATO mission, set for launch on a Soyuz rocket by 2024, won a competition among five candidate projects, besting another planet-hunting telescope concept and proposals to observe black holes, probe the relationship between gravity, matter and time, and retrieve samples from a near-Earth asteroid.

ESA decided on PLATO on the recommendation of senior European scientists impaneled to review the missions on technical and budget grounds.

Stationed at the L2 Lagrange point a million miles from the night side of Earth, PLATO will sweep across two regions of the sky and monitor stars for dips in brightness, an indicator of a planet passing between the spacecraft and the star.

The precision of PLATO’s imaging detectors will also allow scientists to observe fluctuations in starlight stemming from processes inside the stars, a field known as astroseismology. The mission will determine the age, radius and mass of each planet’s host star.

The planet-hunting mission, expected to discover and study thousands of worlds, is tailored to seek the signatures of small rocky planets in the habitable zone, a region where temperatures are just right to support liquid water and life.

“We want to completely characterize low-mass planets out to the habitable zones, learn about their internal composition, the density, and the age of the system,” said Stephane Udry, an astronomer at the University of Geneva, in a presentation of the mission in November.

Udry said PLATO will provide a “huge number” of planets for observations by future facilities, such as the European Southern Observatory’s European Extremely Large Telescope and the James Webb Space Telescope, which could reveal the nature of their atmospheres and chemical make-up.

Unlike Kepler, which imaged a narrow swath of the sky in the constellations Lyra and Cygnus, PLATO will scan two wide fields, staring at each for up to three years and collecting and analyzing light from a million stars.

“The idea is to observe two big fields for a very long time and use a step-and-stare phase to cover nearly half the sky,” Udry said.

The PLATO observatory will actually consist of 34 telescopes, creating an imaging array to simultaneously observe bright and dim objects, according to scientists.

Heike Rauer, a scientists with the German space agency DLR, leads the pan-European PLATO mission consortium.

“PLATO will begin a completely new chapter in the exploration of extrasolar planets,” Rauer said in a press release. “We will find planets that orbit their star in the life-sustaining ‘habitable’ zone: planets where liquid water is expected, and where life as we know it can be maintained.”

PLATO is the third medium-class mission in ESA’s Cosmic Vision program, a strategic initiative guiding the selection of solar system exploration and astrophysics missions. It follows the Solar Orbiter mission, a joint project between ESA and NASA scheduled for launch in 2017, and the Euclid observatory launching in 2020 to map the influence of dark energy on the evolution of the universe.

ESA passed over PLATO in the selections of Solar Orbiter and Euclid.

PLATO is under a European Space Agency cost cap of 600 million euros, or about $820 million. ESA member states and international partners such as NASA will likely add contributions beyond the cost limit.

PLATO stands for PLAnetary Transits and Oscillations of stars. The project has similar objectives to ESA’s canceled Eddington mission, which was shelved more than a decade ago to save money.

“In the last 20 years more than one thousand exoplanets have been discovered, with quite a few multi-planetary systems among them,” Rauer said. “But almost all of these systems differ significantly from our solar system in their properties, because they are the easiest-to-find examples. PLATO firmly will establish whether systems like our own solar system, and planets like our own Earth are common in the galaxy.”

Follow Stephen Clark on Twitter: @StephenClark1.