An artist's concept depicts Kepler-69c, a planet 1.7 times the size of Earth that orbits in the habitable zone of a star like our sun, located about 2,700 light-years from Earth in the constellation Cygnus.
On April 29, the European Space Agency announced that its premier infrared space observatory had run out of coolant and the mission had come to an end. Observing the cosmos in far-infrared wavelengths, the space telescope has given us some of the most striking views of cool nebulae, star forming regions, comets being pulverized around nearby stars, even asteroids buzzing around our own solar system. As we say goodbye to the historic mission, and astronomers continue to analyze the huge wealth of data Herschel has left us with, it's time to have a look back at some of the mission's most spectacular observations.
In this picture, embryonic stars feed on the gas and dust clouds deep inside the Orion Nebula. This image combines far-infrared data by Herschel and mid-infrared data by NASA's Spitzer space telescope.
ESA/Herschel/PACS & SPIRE Consortium, O. Krause, HSC, H. Linz
The Andromeda galaxy in infrared -- Herschel took this portrait of the famous spiral galaxy, picking out the fine detail from gas and dust running through its structure.
ESA/PACS & SPIRE consortia, A. Rivera-Ingraham & P.G. Martin, Univ. Toronto, HOBYS Key Programme (F. Motte)
This three-color image of the W3 giant molecular cloud combines Herschel's 70 μm (blue), 160 μm (green) and 250 μm (red) filters. W3 is located about 6200 light-years away and is a hub of intense star formation. Filaments of gas and dust cocooning protostars (yellow dots) can be seen.
ESA/Herschel/PACS/L. Decin et al
The star Betelgeuse is observed in infrared by Herschel as it rapidly approaches a "barrier" of interstellar gas. The bow shock of the star's stellar winds can easily be seen.
ESA/Bonsor et al (2013)
The star Kappa Coronae Borealis is captured in this infrared observation by Herschel. The star itself is blocked out whereas the ring of debris (likely from asteroid/comet impacts) glows bright.
ESA/Herschel/PACS/Bram Acke, KU Leuven, Belgium
The infrared emissions from dust produced by a huge number of cometary collisions surrounding the famous star Fomalhaut glows in bright blue in Herschel's eye. At least one exoplanet is known to orbit within this ring of dust.
Herschel: Q. Nguyen Luong & F. Motte, HOBYS Key Program consortium, Herschel SPIRE/PACS/ESA consortia. XMM-Newton: ESA/XMM-Newton
Supernova remnant W44 is the focus of this observation created by combining data from ESA's Herschel and XMM-Newton space observatories.
ESA and SPIRE & PACS consortia, Ph. André (CEA Saclay) for Gould’s Belt Key Programme Consortia
Herschel picks out 600 newly forming stars inside the W40 nebula cradle of stars -- located 1,000 light-years away in the constellation Aquila.
ESA/Herschel/PACS/MACH-11/MPE/B.Altieri (ESAC) and C. Kiss (Konkoly Observatory)
Herschel could also study solar system objects with ease. In this observation, asteroid Apophis was captured during its approach to Earth on 5/6 January 2013. This image shows the asteroid in Herschel’s three PACS wavelengths: 70, 100 and 160 microns, respectively.
ESA/Herschel/PACS, SPIRE/N. Schneider, Ph. André, V. Könyves (CEA Saclay, France) for the “Gould Belt survey” Key Programme
This striking image complemented Hubble's 23rd anniversary optical view of the Horsehead Nebula. Herschel's infrared observation of the Orion Molecular Cloud complex (including the Horsehead Nebula -- visible far right of image) provided a unique perspective on this astronomical favorite.
Until we understand the limits of life, it will be difficult to determine if alien planets can host any living beings, scientists say.
By studying Earth-bound "extremophiles" — microbes that survive in harsh conditions, such as hot and acid-filled ocean vents — scientists can understand the limits of temperature, pressure and acidity that support life on Earth more fully. These finding may also be applied to other planets.
These life-supporting parameters could be revised, however, if a new extremophile is discovered or biology is different on another world, said John Baross, a researcher at the University of Washington who focuses on these microbes, on March 17. [Extreme Life on Earth: 8 Bizarre Creatures]
"This is very much a discovery-based science, and there is so much we still don't understand," Baross said during the Search for Life Beyond the Solar System conference in Tucson, Ariz.
One emerging field of research examines microbes living in a low carbon and energy environment, like the parts of the ocean below where sunlight can reach through the waters.
Considering slower evolution over millions of years in these reaches is a "totally new ballgame" for alien planet researchers, Baross said.
Musings on life beyond Earth
Hosts for the conference include the University of Arizona's Steward Observatory as well as the Vatican Observatory, which is based just outside of Rome. Historically, science and religion have at times come to loggerheads at the Vatican. For example, when Galileo Galilei discovered moons around Jupiter in 1610, he said the Earth orbits sun rather than the other way around, in defiance of the church.
The Vatican Observatory has made its own contributions to astronomy, pointed out José Funes, its current director. The 19th-century director Angelo Secchi was one of the first scientists to authoritatively say that the sun is a star, Funes said.
An artist's concept depicts Kepler-69c, a planet 1.7 times the size of Earth that orbits in the habitable zone of a star like our sun, located about 2,700 light-years from Earth in the constellation Cygnus.NASA/Ames/JPL-Caltech
Secchi, like scientists today, also mused on the possibility of life beyond Earth, a theme that Vatican scientists discussed at the conference, Funes added, putting a passage from Secchi's 1870 book, "Le Soleil" (The Sun) on the screen.
"What to think of these stars without any doubt similar to our sun," the passage read, "destined like the sun to keep alive an enormous quantity of creatures of every kind?"
Finding alien life will be a complex task, other scientists pointed out. Perhaps extraterrestrials will require a "wet" planet like Earth and a "dry" planet like Mars to pass material back and forth, said biochemist Steven Benner of The Westheimer Institute for Science and Technology in Florida.
Benner suggested that it might be easier for organisms to come alive in a dry environment, but that it would take water to make sustained life possible.
Other researchers, meanwhile, are trying to better understand the parameters of life by creating synthetic lifeforms to see how they will behave in different environments. Lynn Rothschild of NASA's Ames Research Center, is the faculty adviser for Brown University and Stanford University students participating in the annual International Genetically Engineered Machine competition.
Using DNA samples in a library, the students build artificial systems meant to address certain scientific questions like how to be more resistant to radiation. This can help supplement research on extremophiles where "there are not a lot of studies," Rothschild said.
More From LiveScience:
The Search for Life on Mars (A Photo Timeline)
Strangest Places Where Life Is Found On Earth
Alien Planet Quiz: Are You an Exoplanet Expert?
This story originally appeared on LiveScience.com.
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