The possible existence of Earth-like Binary Planets

The possible existence of Earth-like binary planets is being described today at the American Astronomical Society's Division for Planetary Sciences meeting in Tucson, AZ. 

Two bodies, each of mass similar to Earth, can form a closely orbiting pair under certain conditions present during the formation of planetary systems.

This theoretical proposal is completely unlike the Earth-Moon system or Pluto-Charon, where the two bodies are very different in mass, and arises in some "kissing" collisions where two similar mass bodies encounter each other and become a bound system because of the energy lost in the strong tides raised on each other in the encounter.

The resulting binary can then persist for billions of years provided it forms well away from the central star, at half an astronomical unit (the distance between the Earth and Sun) or more.

This work was presented by undergraduate Keegan Ryan, graduate student Miki Nakajima, and Dr. David Stevenson of the California Institute of Technology in Pasadena, CA.

The result does not contradict existing data for planets around other stars but suggests that future data may uncover such systems.

This is the first such study to examine the possibility of terrestrial binary planets.

During the formation of terrestrial planets, large rocky bodies orbiting around a star occasionally get close enough to interact with one another.

If two bodies collide head on or obliquely, then this interaction typically results in accretion where the two bodies merge to form a larger one, perhaps leaving behind a disk of debris from which a moon can form.

This is the standard picture for how Earth got its moon and a possible explanation for Pluto's moon, Charon.

If the two bodies collide in a grazing manner but at high velocity, then the two bodies "hit and run" and separate from one another once again, failing to form a bound pair.

The research presented today searched for a middle ground, a scenario in which the interaction results in two large bodes that do not merge but still remain locked in orbit.

This configuration, termed a terrestrial binary planetary system, would necessarily evolve into a state where the two bodies are tidally locked and with the centers of the two planets being separated by only three or so planet radii.

NB: With orbital period being almost the same as day length for both planets.

There is a good reason to believe terrestrial binary planetary systems may be possible.

In a grazing collision the angular momentum is too high to be contained within a single rotating body (it would fission) and if the bodies barely touch then they could retain their identity.

However, it requires an encounter where the bodies are initially approaching each other at low enough velocity.

To test for this possibility, a simulation technique called Smoothed Particle Hydrodynamics (SPH) was utilized.

Smoothed Particle Hydrodynamics represents a body as a collection of tens of thousands of particles, and it has been used to study protoplanetary collisions as well as the giant impact hypothesis of the Moon's formation.

Using SPH, collisions between two rocky Earth-sized bodies were simulated, with impact velocity and impact parameter (a measure of how head-on a collision is) being varied and the output observed.

In the cases where the bodies underwent substantial collision, the scientists replicated previous results in which a binary system did not arise but a moon might form.

However, by including interactions where the bodies are close enough to undergo a large tidal distortion, initial conditions were found that led to a terrestrial binary planetary system.

Search for Life Suggests Alien Solar Systems More Habitable than Ours

Scattered around the Milky Way are stars that resemble our own sun—but a new study is finding that any planets orbiting those stars may very well be hotter and more dynamic than Earth.

That’s because the interiors of any terrestrial planets in these systems are likely warmer than Earth—up to 25 percent warmer, which would make them more geologically active and more likely to retain enough liquid water to support life, at least in its microbial form.

The preliminary finding comes from geologists and astronomers at Ohio State University who have teamed up to search for alien life in a new way.

They studied eight “solar twins” of our sun—stars that very closely match the sun in size, age, and overall composition—in order to measure the amounts of radioactive elements they contain.

Those stars came from a dataset recorded by the High Accuracy Radial Velocity Planet Searcher spectrometer at ESA's European Southern Observatory in Chile.

They searched the solar twins for elements such as thorium and uranium, which are essential to Earth’s plate tectonics because they warm our planet’s interior.

Plate tectonics helps maintain water on the surface of the Earth, so the existence of plate tectonics is sometimes taken as an indicator of a planet’s hospitality to life.

Of the eight solar twins they’ve studied so far, seven appear to contain much more thorium than our sun—which suggests that any planets orbiting those stars probably contain more thorium, too.

That, in turn, means that the interior of the planets are probably warmer than ours.

“If it turns out that these planets are warmer than we previously thought, then we can effectively increase the size of the habitable zone around these stars by pushing the habitable zone farther from the host star, and consider more of those planets hospitable to microbial life,” said Ohio State doctoral student Cayman Unterborn, who presented the results at the American Geophysical Union meeting in San Francisco this week.

“At this point, all we can say for sure is that there is some natural variation in the amount of radioactive elements inside stars like ours,” he added.

“With only nine samples including the sun, we can’t say much about the full extent of that variation throughout the galaxy. But from what we know about planet formation, we do know that the planets around those stars probably exhibit the same variation, which has implications for the possibility of life.”

His advisor, Wendy Panero, associate professor in the School of Earth Sciences at Ohio State, explained that radioactive elements such as thorium, uranium, and potassium are present within Earth’s mantle. These elements heat the planet from the inside, in a way that is completely separate from the heat emanating from Earth’s core.


Read more of this article at scienceblog.com

NASA’s Kepler Spacecraft Discovers 2 Earth-Size Planets

NASA's Kepler mission announces that it's found two planets circling another star, the first ever that are Earth's size or smaller. In this artist's conception, the planet Kepler-20f, which could have an atmosphere of water vapour, is compared to Earth. (Courtesy Tim Pyle via Nature)

In what amounts to a kind of holiday gift to the cosmos, astronomers from NASA’s Kepler spacecraft announced Tuesday that they had discovered a pair of planets the size of Earth orbiting a distant star.

The new planets, one about as big as Earth, the other slightly smaller than Venus, are the smallest planets yet found beyond the solar system. Unfortunately, they are not in the 'Goldilocks' zone.

Astronomers said the discovery showed that Kepler could indeed find planets as small as our own and was an encouraging sign that planet hunters would someday succeed in the goal of finding Earth-like abodes in the heavens.

Since the first Jupiter-size exoplanets, as they are known, were discovered nearly 15 years ago astronomers have been chipping away at the sky, finding smaller and smaller planets.

“We are finally there,” said David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics, who was a member of the team that made the observations, led by his colleague Francois Fressin.

The team reported its results in an online news conference Tuesday and in a paper being published in the journal Nature.

The announcement doubled the number of known Earth-size planets in the galaxy to four from two — Earth and Venus.

The next major goal in the planetary hunt, astronomers say, is to find an Earth-size planet in the so-called Goldilocks zone of a star, where conditions are temperate for water and thus life.

The two new planets, called Kepler 20e and Kepler 20f, are far outside the Goldilocks zone — so close to the star, termed Kepler 20, that one of them is roasting at up to 1,400 degrees Fahrenheit — and are thus unlivable.

Although the milestone of an Earth-size planet had long been anticipated, astronomers on and off the Kepler team were jubilant.

Geoffrey Marcy of the University of California, Berkeley, another Kepler team member, called the new result “a watershed moment in human history.”

Debra Fischer, a planet hunter from Yale, who was not part of the team, said, “This technological feat is incredibly important because it means that the detection of Earth-sized planets at larger distances is technically possible


Read more here

MARS Rover Curiosity: Astrobiologists Claim Parts Of Mars May Be Habitable

Astrobiological researchers have discovered significant regions below the surface of Mars that could be habitable for Earth-based life.

“Our models tell us that if there is water present in the Martian sub-surface then it could be habitable – as an extensive region of the subsurface is at temperatures and pressures comfortable for terrestrial life,” said the lead author Eriita Jones in a press release.

Their research, which is published today in the journal Astrobiology, could serve as a guide to future Martian exploration missions that are looking for indigenous Martian life.

However, current Mars rovers don’t have the capability to dig deep enough to test the researchers’ findings.

In an earlier paper, the same researchers applied a statistical technique to the Earth to determine where life existed on Earth and where it didn’t.

They then used the techniques from that earlier study and applied them to Mars. What they found is that about 3% of the total volume of Mars is capable of supporting Earth-based lifeforms.

That may not sound like a lot – until you consider that only 1% of the Earth’s volume is inhabited.

It will be interesting to see if future generations of Martian rovers will have the capability to follow up on this research.

I’d be curious to see if the new rover, Curiosity, will be near one of the regions that these researchers uncovered. One of that rover’s goal is to look for ideal places for future rover missions to search for life.

If Curiosity is able to find any signs of life at all near regions identified in this paper, that would make it an excellent roadmap for future Martian missions.

Saturn Moon: Titan Reveals Surprisingly Earth-Like Features

Global mosaic of Visual and Infrared Mapping Spectrometer (VIMS) images acquired during the nominal and equinox Cassini mission. 

Differences in composition translate into subtle differences of colors in this mosaic, revealing the diversity of terrains on Titan, such as the brownish equatorial dune fields or the bright, elevated terrains.

CREDIT: JPL/NASA/Univ. of Arizona/CNRS/LPGNantes

After meticulously stitching together images that were gathered over six years by a NASA spacecraft in orbit around Saturn, astronomers have created a global map of the surface of Titan, the ringed planet's largest moon, and it features some surprisingly Earth-like geological features.

An international team of astronomers, led by the University of Nantes in France, created the striking mosaic of Titan's surface using infrared images taken by the Visual and Infrared Mapping Spectrometer (VIMS) aboard NASA's Cassini spacecraft.

The global map and animations were presented Tuesday (Oct. 4) at the European Planetary Science Congress and the American Astronomical Society's Division of Planetary Science in Nantes, France. [See global map and video of Titan's surface]

NASA: Scientists very excited by Earth-like Planet Discovery

Meet GJ 1214b, the most Earth-like planet ever found outside our solar system.

It’s not exactly Earth’s twin: It’s about six times bigger, a whole lot hotter and made mostly of water.

But compared to the giant gas balls that account for nearly every other extrasolar planet ever found, it’s pretty darn close.

And through a fortunate happenstance of cosmic geometry, astronomers will be able to study GJ 1214b in great detail.

“If you want to describe in one sentence what this planet is, it’s a big, hot ocean,” said Harvard University astronomer David Charbonneau. “We can even study its atmosphere. This planet will occupy us for years. That’s part of what’s so exciting about it.”

Described by Charbonneau and 17 other astronomers in a paper published Wednesday in Nature, GJ 1214b is the latest of roughly 400 planets detected by earthly telescopes. Of these, 28 are considered “super-Earths” — planets with a mass roughly comparable to our own.

The super-Earths themselves are too distant to be seen. Instead, astronomers infer their presence from subtle distortions in starlight, caused when photons travel through the super-Earths’ gravitational fields. Depending on the degree of distortion, astronomers can even calculate a planet’s mass.

That’s how Corot-7b, a rocky planet with roughly twice the heft of Earth, was spotted in February. Ditto Gliese 581c, identified two months later, and orbiting its star at a distance consistent with human notions of habitability.

Unfortunately, not much more will ever be known about those planets. Corot-7b is 500 light-years away, too distant for our telescopes to discern more detail. And from our viewing angle, Gliese 581c never quite crosses directly in front of its sun, causing photons to warp in ways that would reveal its atmospheric character.

GJ 1214b does pass in front of its sun. Separated from Earth by a distance of just 42 light years, it’s close enough to be studied. Scientists will finally get to look at another Earth-like world.


“Only rarely does a long-sought scientific frontier loom so prominently just beyond the horizon, that the next generation of instruments seems sure to reach it,” wrote Geoffrey Marcey, a University of California, Berkeley astronomer, in a commentary accompanying the findings. “They provide the most-watertight evidence so far for a planet that is something like our own Earth, outside our solar system.”

Based on its radius and mass — about 2.7 and 6.6 times that of Earth’s — Charbonneau and the other astronomers have calculated GJ 1214b’s density. It appears to be composed of extraordinarily deep oceans, surrounding a rocky core.

The planet’s atmosphere and precise composition remain a mystery, but it’s likely composed of many of the same elements found elsewhere at sites of planetary formation, in swirling disks of dust and gas that have yet to accrete: hydrogen, helium, nitrogen, magnesium, oxygen, carbon.

That list of ingredients raises at least the possibility of life. With an estimated temperature of 370 degrees Fahrenheit, GJ 1214b is an unlikely incubator (Earth’s toughest extremophile, a microbe that lives in deep-sea volcanic vents, maxes out at 284 degrees) but it’s not impossible.

“I don’t want to imply that there’s any indication of life as we know it. It might have life, but it would have to be a strange kind of life,” said Charbonneau.

The telescopes sure to be trained on GJ 1214b in the near future will try to answer that question. But even if it proves barren, other planets await. The telescopes that spotted GJ 1214b were custom designed to find Earth-like planets around nearby stars, and had only operated for a few months before striking water.

“We only look at a handful of stars before finding this planet, said Charbonneau. “Either we got lucky, or the planets are very common.”