‘Old Earths': the search for ancient and habitable (but dying) exoplanets

Illustration depicting the life cycle of Sun-like stars. Billions of years from now, our own Sun will expand into a red giant star, scorching any life that exists. Image Credit: ESO/M. Kornmesser
Illustration depicting the life cycle of Sun-like stars. Billions of years from now, our own Sun will expand into a red giant star, scorching any life that exists. Image Credit: ESO/M. Kornmesser

Researchers at Cornell University are taking a new approach to the search for alien life: looking for habitable planets older than Earth, “old Earth analogues,” which may be nearing the end of their habitable lifetimes. Astronomers would search for biosignatures from worlds much older than Earth, where lifeforms are dying off due to circumstances such as the planet’s star expanding in its old age, gradually heating the planet to a point where life is no longer possible.

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Curiosity rover finds more evidence for possible liquid water brines on Mars

The Rover Environmental Monitoring Station (REMS) on the Curiosity rover, used to make the brine calculations. Photo Credit: NASA/JPL-Caltech/MSSS
The Rover Environmental Monitoring Station (REMS) on the Curiosity rover, used to make the brine calculations. Photo Credit: NASA/JPL-Caltech/MSSS

The search for liquid water on Mars is one that has been on-going for decades. It can’t exist for long on the surface, as it will quickly sublimate into the cold, thin atmosphere. Aquifers deep below the surface are still possible, but there is also another tantalizing possibility which scientists have been considering: brines. Such salty liquid water could theoretically last a bit longer on the surface or in the near-subsurface, and now the Curiosity rover has provided more evidence that this may indeed be happening at its location in Gale Crater, as well as elsewhere.

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Scientists create colour-based catalogue of Earthly life forms to help search for alien biology

A hypothetical rendering of colorful plant life on a habitable exoplanet. Although most such alien life, if it exists, found with this technique may be microscopic, it illustrates how analysis of color could help scientists learn more about the physical nature of alien biology. Image Credit: NASA/Caltech/Doug Cummings
A hypothetical rendering of colourful plant life on a habitable exoplanet. Although most such alien life, if it exists, found with this technique may be microscopic, it illustrates how analysis of colour could help scientists learn more about the physical nature of alien biology. Image Credit: NASA/Caltech/Doug Cummings

With exoplanets now being discovered by the thousands, and estimated to be in the billions in our galaxy alone, attention is naturally turning to how astronomers might be able to search for evidence of life on any of those far-away worlds. Now, a team of scientists is taking a novel approach to doing just that, by creating a colourful catalogue of reflection signatures of various life forms on Earth. The new database and research was just published in the March 16 Proceedings of the National Academy of Sciences.

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Cassini finds evidence for hydrothermal activity on Saturn’s moon Enceladus

Cutaway view depicting the interior of Enceladus. Water, salts, organics, and methane make their way from the hydrothermal vents on the ocean bottom to the surface through cracks in the icy crust, erupting as geysers. Image Credit: NASA/JPL
Cutaway view depicting the interior of Enceladus. Water, salts, organics, and methane make their way from the hydrothermal vents on the ocean bottom to the surface through cracks in the icy crust, erupting as geysers. Image Credit: NASA/JPL

The deep oceans on Earth are teeming with life, despite the cold and darkness, thanks to hydrothermal vents which provide needed heat and nutrients in an otherwise rather uncomfortable environment. Now, the first evidence has been found for current hydrothermal activity elsewhere in the Solar System: on the ocean bottom of Saturn’s moon Enceladus.

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New technique to study clouds on exoplanets developed by researchers at MIT

Artist’s conception of clouds on Kepler-7b. Image Credit: NASA (edited by Jose-Luis Olivares/MIT)
Artist’s conception of clouds on Kepler-7b. Image Credit: NASA (edited by Jose-Luis Olivares/MIT)

While exoplanets are now being discovered by the thousands, it is still a painstaking process to determine any specific details about them, since they are so incredibly far away. However, astronomers have been devising new techniques to do just that, including one that makes it easier to analyze the property of clouds on some of these distant worlds.

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‘Life not as we know it': new research shows how exotic biology may be possible on Titan

Illustration of methane rainfall and lake on Titan. New research suggests exotic forms of life could be possible in this alien environment. Image Credit: Mark Garlick (Space-art.co.uk)/APOD
Illustration of methane rainfall and lake on Titan. New research suggests exotic forms of life could be possible in this alien environment. Image Credit: Mark Garlick (Space-art.co.uk)/APOD

The search for life elsewhere has long focused on what we are most familiar with on Earth – in other words, “life as we know it,” or organisms which are carbon-based and require water to survive. However, a growing number of scientists are now thinking that alternative forms of life are possible, ones which have never been seen on Earth, but could flourish in other types of alien environments. A new study from Cornell University addresses this very question, demonstrating a form of microscopic life which would be possible on Saturn’s largest moon Titan.

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Scientists debate how to search for life on Europa in new mission

Jupiter’s ice-covered moon Europa hides a water ocean beneath its surface. A return mission is now planned to help search for evidence of life there. Photo Credit: NASA/JPL
Jupiter’s ice-covered moon Europa hides a water ocean beneath its surface. A return mission is now planned to help search for evidence of life there. Photo Credit: NASA/JPL

Jupiter’s moon Europa, with its subsurface ocean, is considered by many to be the best place in the Solar System to search for extraterrestrial life. With NASA now committing itself to a new mission sometime in the 2020s, the focus is turning to what would be the best strategy for looking for any life which may be there. Over 200 scientists and engineers met at NASA’s Ames Research Center in Mountain View, Calif., last week for a workshop called The Potential for Finding Life in a Europa Plume to do just that.

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Exploring an alien sea: NASA designs submarine to send to Titan

Artist’s conception of the Titan Submarine Phase I Conceptual Design. Much like submarines on Earth, the sub would explore the depths of one of Titan’s methane/ethane seas. Image Credit: NASA
Artist’s conception of the Titan Submarine Phase I Conceptual Design. Much like submarines on Earth, the sub would explore the depths of one of Titan’s methane/ethane seas. Image Credit: NASA

Who wouldn’t want to go explore an alien sea? It seems that NASA would certainly like to, and the agency has unveiled a new submarine design to hopefully do just that one day. The submarine would be sent to Saturn’s largest moon, Titan, to dive into one of the large liquid methane seas on the moon’s frigid surface; such a mission idea may sound like science fiction, but it’s not, and would be the first ever to explore a sea on another world which is both Earth-like in some ways, yet utterly alien in others.

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Cassini data indicates Enceladus’ ocean similar to soda lakes on Earth

The geysers of Enceladus, erupting through cracks in the ice at the south pole from a subsurface salty ocean or sea. Image Credit: NASA/JPL
The geysers of Enceladus, erupting through cracks in the ice at the south pole from a subsurface salty ocean or sea. Image Credit: NASA/JPL

Along with Jupiter’s infamous moon Europa, Saturn’s moon Enceladus is one of the most fascinating places in the Solar System, with its huge geysers of water vapour erupting from cracks in the surface at the south pole. The massive plumes are now thought to originate in a subsurface ocean or sea of salty liquid water, similar perhaps to Europa’s underground ocean. Now, new analysis is providing a more detailed look at the chemical makeup of this unique alien environment and its potential to support life.

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‘Super-Earth’ exoplanets may be more Earth-like than previously thought

Artist's conception of an Earth-like super-Earth exoplanet, taken from a video still. Credit: Kepler/NASA
Artist's conception of an Earth-like super-Earth exoplanet, taken from a video still. Credit: Kepler/NASA
Artist’s conception of an Earth-like super-Earth exoplanet, taken from a video still. Credit: Kepler/NASA

With the number of known exoplanets being discovered now numbering in the thousands (and estimated to be in the billions in our galaxy alone), astronomers have already found an amazingly diverse plethora of worlds. Some of the most common are the “super-Earths,” rocky planets which are larger than Earth but smaller than Neptune or Uranus. It has been thought by scientists that such worlds might often be true water worlds, with their surfaces completely covered by water with no land visible at all, causing less stable climates than on our home planet.

But now new studies suggest that these planets might tend to be more Earth-like after all. Two scientists, Nicolas B. Cowan from Northwestern University and Dorian Abbot from the University of Chicago have announced a new model for super-Earths which shows that ones which are tectonically active would probably store most of their water in their mantles, producing both oceans and continents and subsequently a more Earth-like climate. This would likely be true regardless of the mass of the planet(s).

As Cowan explains:

“Are the surfaces of super-Earths totally dry or covered in water? We tackled this question by applying known geophysics to astronomy.

Super-Earths are expected to have deep oceans that will overflow their basins and inundate the entire surface, but we show this logic to be flawed. Terrestrial planets have significant amounts of water in their interior. Super-Earths are likely to have shallow oceans to go along with their shallow ocean basins.”

Plate tectonics allow a water cycle to exist between the oceans above and the mantle below, which helps to stabilize the climate. Even for such rocky planets larger than Earth, this could still create both oceans and continents, due to increased gravity and seafloor pressure.

“We can put 80 times more water on a super-Earth and still have its surface look like Earth,” Cowan said. “These massive planets have enormous seafloor pressure, and this force pushes water into the mantle.”

On Earth, the carbon cycle, essential for life as we know it on our planet, is also regulated by surface temperatures, producing a stabilizing feedback, a sort of thermostat on geological timescales.

As Abbot notes, “Such a feedback probably can’t exist in a waterworld, which means they should have a much smaller habitable zone. By making super-Earths 80 times more likely to have exposed continents, we’ve dramatically improved their odds of having an Earth-like climate.”

The findings suggest that super-Earths are much more likely to have an Earth-like surface than previously thought. The new model depends on these planets have plate tectonics and a similar amount of water, or more, stored in their mantles, which are still two unknowns at this point. But the odds are probably good that at least some of them will, increasing the chances of life of some sort on these worlds.

The findings were presented on Jan. 7 at the 223rd meeting of the American Astronomical Society (AAS) annual meeting in Washington, D.C.

This article was first published on Examiner.com.

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