Today was another big day for those interested in space exploration, and the search for other Earth-like alien worlds in particular – the first Earth-sized exoplanet orbiting another star in the habitable zone has been discovered, it was announced by astronomers with the Kepler space telescope mission.
Category Archives: Astrobiology
Coming just after the news of the ringed asteroid and new dwarf planet, some more exciting news from the outer Solar System was announced last Thursday, and this will be of particular interest to those hoping to find evidence of alien life elsewhere in our solar system. Saturn’s tiny moon Enceladus, famous for its geysers of water vapour spewing out into space, has long been suspected of harboring an internal ocean, just like Jupiter’s moon Europa (and possibly others). Now it seems that scientists have the evidence they’ve been looking for, thanks to new findings based on data returned by the Cassini spacecraft, still in orbit around Saturn.
For scientists and space enthusiasts who have been advocating a mission to Jupiter’s moon Europa, there was some good news this week from NASA. A mission to Europa has been officially included in the NASA 2015 Budget request. The inclusion is a reason for cautious optimism; while naming it as a target for a future robotic mission in the 2020s, NASA also wants to do that mission as cheaply as possible. Given the current economic climate, that may not be surprising, but what would reduced cost mean in terms of science?
The debate over possible evidence for life on Mars is one of the most hotly debated subjects in space science, and some news released today, February 27, is sure to add fuel to the fire. Studies of a Martian meteorite, known as Yamato 000593 (Y000593), have revealed signs of past liquid water activity as well as possible evidence of actual biological processes.
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.
Europa has been in the news a lot this past week, with the discovery of apparent plumes of water vapour erupting from its surface, similar to those on Saturn’s moon Enceladus. An exciting find, given that this moon has a global ocean of water covered by its icy crust. There was also the first detection of clay-type minerals on Europa’s surface. Now, another discovery shows that Europa may be similar to Earth in yet another way – the first other known world to have active plate tectonics, it was announced last Friday at the American Geophysical Union meeting in San Francisco.
Why is this significant? Plate tectonics can provide a way for nutrients to be carried from the surface down into the waters below, just as they do on Earth.
According to planetary scientist Alyssa Rhoden, a NASA postdoctoral program fellow, “What’s exciting is that this would be the only other place outside of Earth where a plate-tectonic-style system is occurring.”
Scientists have known for some time that Europa has a relatively young surface which is being replenished somehow by new, fresh ice. It is thought that this ice is coming up through features called dilational bands, which are long cracks on the surface. There are thousands of them, making Europa look like a giant cracked eggshell. The new ice also keeps Europa’s surface remarkably smooth with very few craters.
New studies now suggest that the dilational bands behave in a similar way to Earth’s tectonic plates. New ice rises up through the cracks to the surface, but where does the old ice go?
Planetary scientist Simon Kattenhorn of the University of Idaho explained what they think is happening during their presentation for the AGU meeting:
“Unless Europa has been expanding within the last 40 to 90 million years, there has to be some process on this icy moon that’s able to accommodate a large amount of new surface area being created at dilational bands.”
That process would be similar to what happens along mid-ocean ridges on Earth, where crustal tectonic plates meet together. New crust, or in Europa’s case, ice, is forced upward through the spaces between the plates where it forms newer crust. Older crust in turn is then forced back down into the Earth’s mantle in places where a continental plate meets an oceanic plate. In this process, called subduction, the oceanic plate is pushed below the continental plate. This whole exchange is an efficient global recycling between old and new material.
Now for the first time, what appear to be subduction zones have been identified on Europa as well, by Kattenhorn and his colleagues. This is important, since organic material, also just found on Europa’s surface for the first time, and nutrients could then have a way of making it down below the surface and into the water deep below. This of course has a direct bearing on the possibility of life in Europa’s ocean. Minerals necessary for life are likely present on the rocky ocean bottom as well since the rocky mantle is thought to be in direct contact with the ocean water just like on Earth.
There may still be another explanation for the observations, but this and other evidence continues to show that Europa is a geologically active little world instead of just a frozen ice ball as once believed. And maybe, just maybe, a living one as well.
This article was first published on Examiner.com.
Europa has intrigued people for decades, ever since the first evidence was found that this small icy moon of Jupiter harbours a subsurface ocean. Additional information about the actual conditions below the surface have been difficult to obtain, since this ocean is covered by a global crust of ice perhaps ten of kilometres thick in places. But perseverance pays off, and now in just this past week there are two new significant discoveries being talked about – evidence from the Hubble Space Telescope for water vapour plumes, announced on Thursday, erupting from Europa’s surface similar to those on Saturn’s moon Enceladus, and the first detection of clay-type minerals on the surface, announced on Wednesday.
Some exciting exoplanet news this week: based on the newest data from the Kepler space telescope, astronomers now estimate that there are billions of potentially habitable planets in our galaxy which are about the same size as Earth and orbit in the habitable zone of their stars, it was announced yesterday.
Will Curiosity find new clues to ancient Martian habitability, or perhaps even life, at Hematite Ridge?
As the Curiosity rover gets ever closer to its major destination of Mount Sharp, there is an interesting feature there which has become a priority target, one which may help scientists to further study the past habitability of this area, or even provide possible clues to life itself.