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Science Briefs

Earth-like Planets Could Form Earlier than Expected →

Building a terrestrial planet requires raw materials that weren’t available in the early universe. The Big Bang filled space with hydrogen and helium. Chemical elements like silicon and oxygen had to be cooked up over time by stars. But how long did that take? How many of such heavy elements do you need to form planets?

Previous studies have shown that Jupiter-sized gas giants tend to form around stars containing more heavy elements than the Sun. However, new research found that planets smaller than Neptune are located around a wide variety of stars, including those with fewer heavy elements than the Sun. As a result, rocky worlds like Earth could have formed earlier than expected in the universe’s history.

"This work suggests that terrestrial worlds could form at almost any time in our galaxy’s history," said astronomer David Latham . "You don’t need many earlier generations of stars."

Latham and his colleagues examined more than 150 stars known to have planets, based on data from NASA’s Kepler spacecraft. They measured the stars’ metallicities and correlated that with the sizes of the associated planets. Large planets tended to orbit stars with solar metallicities or higher. Smaller worlds, though, were found around metal-rich and metal-poor stars alike.

"Giant planets prefer metal-rich stars. Little ones don’t," explained Latham.

More:

Low-metal stars may nurture many Earth-like worlds
Small Planets’ Evolutionary Edge
Small, rocky planets may be very common in the galaxy
Planets can form around different types of stars
Small Planets Don’t Need Stars with Heavy Metal Content to Form
Other Earths Have Been Around for a While
Small Exoplanets Abound in Diverse Stellar Environments

— 1 year ago
#extrasolar planets 
Some Stars Capture Rogue Planets →

New research suggests that billions of stars in our galaxy have captured rogue planets that once roamed interstellar space. The nomad worlds, which were kicked out of the star systems in which they formed, occasionally find a new home with a different sun. This finding could explain the existence of some planets that orbit surprisingly far from their stars, and even the existence of a double-planet system.

To reach their conclusion, the researchers simulated young star clusters containing free-floating planets. They found that if the number of rogue planets equaled the number of stars, then 3 to 6 percent of the stars would grab a planet over time. The more massive a star, the more likely it is to snag a planet drifting by.

They studied young star clusters because capture is more likely when stars and free-floating planets are crowded together in a small space. Over time, the clusters disperse due to close interactions between their stars, so any planet-star encounters have to happen early in the cluster’s history.

Newborn star systems often contain multiple planets. If two planets interact, one can be ejected and become an interstellar traveler. If it later encounters a different star moving in the same direction at the same speed, it can hitch a ride. A captured planet tends to end up hundreds or thousands of times farther from its star than Earth is from the Sun. It’s also likely to have a orbit that’s tilted relative to any native planets, and may even revolve around its star backward.

More:

Some Planets Are Alien Invaders
Rogue planet adoption

— 2 years ago with 1 note
#extrasolar planets 
A planetary system from the early Universe →

A group of European astronomers has discovered an ancient planetary system that is likely to be a survivor from one of the earliest cosmic eras, 13 billion years ago. The system consists of the star HIP 11952 and two planets. Whereas planets usually form within clouds that include heavier chemical elements, the star HIP 11952 contains very little other than hydrogen and helium. The system promises to shed light on planet formation in the early universe – under conditions quite different from those of later planetary systems, such as our own.

Statistically, a star that contains more “metals” (chemical elements other than hydrogen and helium) – is more likely to have planets. This suggests a question: Originally, the universe contained almost no chemical elements other than hydrogen and helium. Almost all heavier elements have been produced, over time inside stars, and then flung into space as massive stars end their lives in supernovae. So what about planet formation under conditions like those of the very early universe, say: 13 billion years ago? If metal-rich stars are more likely to form planets, are there stars with a metal content so low that they cannot form planets at all? And if the answer is yes, then when, throughout cosmic history, should we expect the very first planets to form?

Now a group of astronomers has discovered a planetary system that could help provide answers to those questions. As part of a survey targeting especially metal-poor stars, they identified two giant planets around a star known by its catalogue number as HIP 11952, at a distance of about 375 light-years from Earth. By themselves, these planets, HIP 11952b and HIP 11952c, are not unusual. What is unusual is the fact that they orbit such an extremely metal-poor and, in particular, such a very old star.

More:

Most Ancient, ‘Impossible’ Alien Worlds Discovered
Planets found at dawn of universe, but their existence is a mystery
How and when did the first planets form in our universe?

— 2 years ago
#extrasolar planets 
Many Billions of Rocky Planets in the Habitable Zones around Red Dwarfs in the Milky Way →

A new result from ESO’s HARPS planet finder shows that rocky planets not much bigger than Earth are very common in the habitable zones around faint red stars. The international team estimates that there are tens of billions of such planets in the Milky Way galaxy alone, and probably about one hundred in the Sun’s immediate neighbourhood. This is the first direct measurement of the frequency of super-Earths around red dwarfs, which account for 80% of 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. The astronomers could estimate how heavy the planets were and how far from their stars they orbited.

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%.

More:

'Super Earths' Abound Nearby
10 Billion Earth-Like Planets May Exist in Our Galaxy

— 2 years ago
#extrasolar planets 
How Many Unbound Planets Roam the Milky Way? →

Life as we know it exists on a cozy planet in a stable orbit around a sun shining brightly in its sky. But a new study hints that the most common life in the universe might exist deep inside eternal-night worlds far from any star, adrift in the icy dark of interstellar space.

Researchers at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University estimate that “nomad” planets, ejected from their home stellar system and now free-floating through the Milky Way, could outnumber stars by as many as 100,000 to 1

— 2 years ago
#extrasolar planets