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X-ray telescope, gravity wave probes to be led by ESA
BY STEPHEN CLARK
ASTRONOMY NOW

Posted: December 2, 2013


The European Space Agency has decided its next two big science missions, each costing more than $1.3 billion, will be a massive X-ray telescope and a long-proposed observatory to confirm the existence of gravitational waves predicted by Albert Einstein's theory of general relativity.


Artist's concept of the Athena+ X-ray telescope. Credit: Athena+ proposal team
 
The missions will not launch until 2028 and 2034, when most of the scientists now involved in the projects will be retired.

The X-ray and gravity wave observatories are not new ideas. Scientists have studied various incarnations of the missions since the 1990s, but financial and technical difficulties have delayed their implementation.

The X-ray telescope will be a successor to NASA's flagship Chandra X-ray Observatory and Europe's XMM-Newton telescope. The gravity mission is a first-of-its-kind project.

European scientists recommended the themes for the next two large-class space science missions, and the chief of ESA's science program confirmed the selections.

ESA officials say the long development timelines are consistent with the agency's other flagship missions, including the Herschel infrared telescope which launched in 2009 after first being studied in 1983. The Gaia mission scheduled for launch Dec. 19 was proposed by scientists in 1993.

Although the objectives of the two flagship science probes are now known, the devil is in the details. The selection of specific concepts, science teams and industrial consortiums is still to come.

The missions must be European-led, but ESA says it welcomes international contributions. Partnerships could come in the form of instruments and detectors, launch vehicles, or operations support.

"We have opened up a new scientific roadmap for Europe today that will establish our leadership in this field for the next two decades while we develop and implement new technologies for these exciting missions," said Alvaro Gimenez, ESA's director of science and robotic exploration.

The missions are part of ESA's "Cosmic Vision" program aimed at collating Europe's space science missions through a judicious selection process tapping the knowledge and aspirations of the European science community.


Artist's concept of a rapidly-spinning supermassive black hole like the one at the center of the Milky Way galaxy. Credit: NASA/JPL-Caltech
 
The Cosmic Vision missions include large- and medium-class probes. The first large mission chosen by ESA in 2012 was the Jupiter Icy Moons Explorer, or JUICE, a spacecraft to conduct flybys of Jupiter's moons Ganymede, Callisto and Europa. JUICE is set for launch in June 2022.

ESA took a different approach for the second and third large-scale Cosmic Vision missions, turning to the science community for proposals to be evaluated and ranked by an independent review panel.

The X-ray telescope and gravity wave missions, provisionally called Athena+ and eLISA, eclipsed 30 other proposals, including concepts for infrared telescopes, an observatory to search for habitable planets around other stars, and white papers on orbiters to Uranus and Neptune.

"We had a difficult task in deciding which scientific themes to choose from all of the excellent candidates, but we believe that missions to study the hot, energetic universe and gravitational waves will result in discoveries of the greatest importance to cosmology, astrophysics, and physics in general," said Catherine Cesarsky, chair of the senior survey committee which picked the winning themes.

The selection process for the X-ray observatory, set for launch in 2028, will begin in early 2014. By the end of the decade, ESA will solicit scientists for detailed designs for the gravity wave mission.

Both themes have been studied by European scientists for years waiting for a chance for a commitment. Although details of the missions have yet to be defined, the proposals sent in for ESA's consideration are based on concepts well-vetted by space agency officials in Europe, the United States and Japan.

"ESA has an outstanding record for developing state-of-the art space observatories that have revolutionized our knowledge of how stars and galaxies were born and evolved," Gimenez said in a press release. "By pursuing these two new themes, we will continue to push back the scientific boundaries and unveil the mysteries of the invisible universe."


Artist's concept of the LISA gravity wave mission. A new version of the LISA mission, known as eLISA, has been proposed by European scientists. Credit: ESA/NASA
 
The X-ray telescope is a follow-up to the International X-ray Observatory, a joint project concept developed by NASA, ESA and the Japan Aerospace Exploration Agency shelved when NASA's funding dried up in 2011.

The Athena+ white paper submitted to ESA last spring proposed an X-ray telescope that could study the formation and growth of supermassive black holes, the gravitational powerhouses at the centers of galaxies like the Milky Way. Likely to be stationed at the gravity-stable L2 Lagrange point a million miles from Earth, the Athena+ proposal would also look back in time to observe how galaxies and galactic clusters assembled a few billion years after the Big Bang.

An X-ray observatory such as Athena+ can only function outside of Earth's atmosphere, revealing how pockets of hot gas in the primordial universe collected to birth galaxies and the most colossal cosmic structures known to astronomers.

Europe's gravity probes will launch in 2034 into an Earth-trailing solar orbit. The three spacecraft, each hosting test masses, will arrange themselves in a nearly equilateral triangle about a million kilometers, or 600,000 miles, apart.

Scientists will monitor slight, but measurable, changes in the distances between the test masses inside the three spacecraft to reveal gravity waves coming from immense objects in the distant universe, such as merging black holes and galactic nuclei.

The novel nature of the gravity mission could also yield fresh insights into the fundamental physics of the universe.

Although the X-ray and gravity missions will be led by Europe, NASA has not ruled out participation as a minor partner.

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