Could there be ‘tens of billions’ of habitable worlds in our own galaxy? That’s the results from a new study that searched for rocky planets in the habitable zones around red dwarf stars. An international team of astronomers using ESO’s HARPS spectrograph now estimates that there are tens of billions of such planets in the Milky Way galaxy, with probably about one hundred in the Sun’s immediate neighborhood, less than 30 light years away.
“Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet,” said Xavier Bonfils, from IPAG, Observatoire des Sciences de l’Univers de Grenoble, France, and the leader of the team. “Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”
This is the first direct estimate of the number of smaller, rocky planets around red dwarf stars. Add this to another recent finding which suggested that every star in our night sky has at least one planet circling it — which didn’t include red dwarf stars – and our galaxy could be teeming with worlds.
This team used the HARPS spectrograph on the 3.6-metre telescope at ESO’s La Silla Observatory in Chile to search for exoplanets orbiting the most common kind of star in the Milky Way — red dwarf stars (also known as M dwarfs). These stars are faint and cool compared to the Sun, but very common and long-lived, and therefore account for 80% of all the stars in the Milky Way.
The HARPS team surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period. A total of nine super-Earths (planets with masses between one and ten times that of Earth) were found, including two inside the habitable zones of Gliese 581 and Gliese 667 C respectively.
By combining all the data, including observations of stars that did not have planets, and looking at the fraction of existing planets that could be discovered, the team has been able to work out how common different sorts of planets are around red dwarfs. They find that the frequency of occurrence of super-Earths in the habitable zone is 41% with a range from 28% to 95%.
Bonfils and his team also found that rocky planets were far more common than massive gas giants like Jupiter and Saturn. Less than 12% of red dwarfs are expected to have giant planets (with masses between 100 and 1000 times that of the Earth).
However, the rocky worlds orbiting red dwarfs wouldn’t necessarily be a good place to spend your first exo-vacation – or for harboring life.
“The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun,” said Stéphane Udry from the Geneva Observatory and member of the team. “But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely.”
Vesta has been viewed as a massive asteroid, but after studying the surface in detail, scientists are describing it as "transitional".
The Dawn spacecraft has been orbiting Vesta - one of the Solar System's most primitive objects - since July 2011.
They have documented many unexpected features on its battered surface.
Mission scientists presented their latest results at the Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas.
Dawn's principal investigator, Christopher T Russell, told the meeting that the science team found it hard not to refer to the object as a planet.
He said the rounded asteroid showed evidence of geological processes that characterise rocky worlds like Earth and the Moon.
Vesta is the second most massive of the asteroids, measuring some 530km (330mi) in diameter. It is dominated by a huge crater called Rheasilvia and bears many other scars left by the hammering it has received at the hands of other asteroid belt denizens.
One important transitional feature of Vesta can be found in its topography, or elevation. Vertical elevation on the Moon or Mars might reach tens of kilometres, but these objects are also very large.
"This means the topography is about 1% of the radius," Dr Ralf Jaumann, from the German Aerospace Center (DLR), told BBC News, "If you go to Vesta, it is 15%, and if you go to the largest outer asteroid - Lutetia - it is 40%."
In short, this mathematical relationship between topography and radius (half an object's diameter), puts Vesta in an intermediate position between small asteroids and rocky planets.
Another aspect concerns the way its surface has been modified, or "processed", by the many collisions. This is evident in dark material that can be seen in images of its terrain.
The dark material seems to be related to impacts and their aftermath. Scientists think carbon-rich asteroids could have hit Vesta at speeds low enough to produce some of the smaller deposits without blasting away the surface.
Higher-speed asteroids could also have collided with Vesta's surface and melted the volcanic basaltic crust, darkening existing surface material.
Scientists are confident there has been volcanism on the asteroid during its history. This is because there are hundreds of pieces of Vesta sitting in museums around the world.
They form a particular class of meteorite called the HEDs; more of these objects have fallen to Earth than all the meteorites from the Moon and Mars put together. Studies of HED meteorites have revealed telling chemical signatures of volcanic activity.
Dave Williams, from Arizona State University, told BBC News: "We know [from the HED meteorites] there were lava flows at some point in history, so I expected there to be at least a few lava flows, maybe a few channels, shields or cones. Looking at all the images in places that have been illuminated thus far, we don't see any evidence of that.
"That's because of all the impact processing over Solar System history. It has destroyed all the evidence."
The male dolphins of Shark Bay, Australia, are known to marine biologists for their messy social entanglements. Their relationships with each other are so unusual — they’re more like the intricate webs of the Mafia than the vertical hierarchies of chimpanzees — that, in a new paper, one team of scientists argues that the dolphins live in a social system that is “unique among mammals.” Intriguingly, the researchers also suggest that these complex, and often cooperative, relationships may stem in part from one simple, unexpected factor: the dolphins’ low cruising speed.
Mammals have evolved a variety of social structures. For example, chimpanzees live in what ethologists call “semiclosed groups”—that is, a community comprised of individuals who are well-known to each other. The members generally aren’t friendly to chimps in other communities; the males practice what’s known as community defense, patrolling and guarding their territory and fighting their neighbors. Inside that tight group, the chimpanzees also have male-male alliances.
At first glance, dolphins seem to have a somewhat similar social system. Two or three adult males form a tight alliance and cooperate to herd a female for mating. (Female dolphins rarely form strong alliances.) Other male teams may try to spirit away the female—particularly if she is in estrus. To fight back, the first-level alliances form partnerships with other first-level alliances, thus creating a larger second-level alliance. Some of these second-level alliances have as many as 14 dolphins and can last 15 years or more. On some occasions, the second-level alliance can call in the troops from yet another group, “a third-order alliance,” as the researchers call them—leading to huge battles with more than 20 dolphins biting and bashing each other with their heads and tails over the right to keep or steal a single female.
But are these dolphin battles analogous to what male chimpanzees do? That is, are the dolphin alliances also fighting over territory? To find out, a research team headed by Richard Connor, a cetacean biologist at the University of Massachusetts, Dartmouth, tracked 12 of the second-order alliances in Shark Bay—a 13,000-square-kilometer bay in western Australia—during the peak mating season from July to November over 6 years. The scientists monitored a 600-square-kilometer region of the bay, keeping tabs on every member in each alliance, the ranges, or areas, they regularly traveled, their behaviors, whether the males had a female with them, and—when there was a battle—which groups came to each other’s aid. Connor’s group then calculated the total home range for each alliance and mapped the degree of overlap between ranges.
The team discovered that, unlike chimps, none of the male groups were patrolling and defending a large community territory. Instead, the dolphins live in a society with a mosaic of many overlapping male and female ranges, without any apparent boundaries. “There isn’t a community border that males or females are patrolling,” says Connor, whose team reports its findings online March 28 in the Proceedings of the Royal Society B. Instead, he says, they live in an open society, with groups teaming up for a bit and splitting apart—all the while doing what Connor summarizes as “soap operatics,” trying to stay on top of who did what to whom, while deciding whether they should stay friends or become foes.
“It’s just unprecedented; there’s nothing like this in other mammal societies,” says Srđan Randić, the study’s lead author and Connor’s former graduate student, who is now a doctoral candidate at Paris University-South XI.
Although bonobos, orangutans, and Western gorillas have less hostile relationships with neighboring groups than do chimpanzees, none of these species has the tolerance of the dolphins, or their ability to form alliances outside of their immediate community. Among mammals, only elephants come close; though they live in matrilineal groups, elephants maintain relationships outside of these, forming large, stratified societies. But even these large societies are still primarily with close kin and are not changeable as are the dolphins’ alliances.
Because female dolphins give birth to only single calves that are separated by several years, the males cannot count on forming alliances with close kin. Instead, male dolphins must learn how to make and maintain friendships—demanding social skills that are likely to have contributed to the dolphins’ large brains, says Connor. But it’s not just the number of social relationships the dolphins must maintain, he adds. “It’s the uncertainty of those third-level alliances. It’s those guys you rarely see. What have they been up to since the last time you met them? Are they still on your side?”
Among mammals, humans, elephants, and dolphins are ranked highly by scientists for their level of social cognition—a convergence that Connor’s team suggests may be due in part to the minimal amount of energy these species expend when just cruising along. The dolphins, they add, offer a model for how a low cruising speed may lead to social smarts. Because the Shark Bay dolphin population is large and has overlapping territories, it doesn’t take long for one group of dolphins moving at their normal speed to meet up with another, possibly competitive, group. In those situations, the dolphins are forced to do the two things that scientists say enhance social cognition: make many friends and form group alliances. Or as Connor puts it, “If you’re going to run into your enemies, you better be with your friends, or have some that are close by, willing to be recruited.”
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