In 2007, two super-Earths known as Gliese 667 C and Gliese 581d were discovered orbiting red dwarfs in the habitable zone, an area in which a planet is able to have surface temperature in order to liquid water. Recently, results from a study suggest these planets plus smaller, rocky ones are quite common in our galaxy and orbit red dwarfs by the tens of billions.

The study was conducted by an international team of scientists a part of the HARPS (High Accuracy Radial velocity Planet Search), ESO’s (European Southern Observatory) planet finder. HARPS’s mission is to detect planets beyond the solar system. HARPS especially aims to discover planets that are in the habitable zone.

In order to calculate the largest amount of Earth-like planets that could exist in the Milky Way, HARPS studied the most common type of star in the galaxy: red dwarfs. Red dwarfs are small, cool, and faint in luminosity in comparison to the Sun. Because they spend less energy than other types of stars, they are long-lived and, therefore, are the most common. Approximately 160 billion exist in the galaxy alone, making up a whopping 80% of the total number of stars.

Using a spectrograph from a 3.6-meter telescope from La Silla Observatory in Chile, HARPS chose a sample of 102 red dwarfs from the southern portion of the sky and studied them for six days. HARPS detected nine super-Earths (planets up to ten times the size of the Earth), two of which were inside the habitable zone. Furthermore, 40% of red dwarfs contain super-Earths that are able to sustain water on their surfaces.

Combining their data and the number of stars without planets, and an estimate of how many planets could be discovered, HARPS was then able to calculate the total number of planets orbiting red dwarfs and the different types of these planets. In the end, their results illustrated that tens of billions of smaller rocky planets exist in the Milky Way.

100 of these hypothesized planets should exist in the immediate vicinity – around 30 light-years – of the Sun (smaller planets are difficult to detect). Massive gassy planets (around the size of Jupiter and Saturn), on the other hand, were calculated to be rare when it came to orbiting red dwarfs.

Although it is exciting knowing that so many Earth-sized orbit stars in the habitable zone, astronomers are not getting their hopes up of finding life. It would be difficult for life to thrive on planets that orbit red dwarfs: because red dwarfs are cool, the habitable zone is rather close, leaving any planets close to the red dwarf to be bombarded with flares of ultraviolet rays and X-rays, making the planets not habitable after all. But that does not daunt astronomers of thinking that any of these small worlds could harbor life.

“Now that we know that there are many super-Earths around nearby red dwarfs,” Xaiver Delfosse, a member of the team tells ESO, “we need to identify more of them using both HARPS and future instruments. Some of these planets are expected to pass in front of their parent star as they orbit — this will open up the exciting possibility of studying the planet’s atmosphere and searching for signs of life.”

A detailed report of HARPS experiment and results can be found here.

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A team of astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA), using NASA’s Hubble Space Telescope, has discovered a “waterworld” planet beyond the solar system.

This exoplanet (i.e. extrasolar planet), dubbed GJ1214b, is located in the constellation Opphiuchus, 40 light-years away from the Earth. It is 2.7 times the size of the Earth and roughly seven times Earth’s weight. At a distance of 1.3 million miles, the watery exoplanet orbits a red dwarf every 38 hours and has a surface temperature of 450º F (230º C).

GJ1214B was first discovered in 2009 by a team of astronomers, led by David Charbonneau of CfA, with the groudbased project MEarth (pronounced “mirth”). Charbonneau and his team were able to detect GJ2124b through transiting, a widely-used method used to search for exoplanets in which one looks to see if a star’s light slightly drops periodically. If it does, a planetary body has traveled in front of the star.

A year later, in 2010, astrophysicist Jacob Bean and his colleagues (also working at CfA) learned that GJ1214b’s atmosphere was chiefly composed of gaseous water. And in 2012, the current group of astronomers working at CfA has confirmed that GJ1214b is indeed veiled in a watery haze.

“GJ1214b is like no planet we know of,” Zachary Berta – an astronomer who is the head of the team – states in CfA’s press release.

Using the parent star’s light, he and his colleagues learned which gases comprise the larger exoplanet’s atmosphere, through which the light passed. With that knowledge, they concluded the GJ1214b and its atmosphere were not mostly made of water, but also hazy – and quite steamy.

The team of was also able to calculate the density of GJ1214b, knowing its size and mass: 2g/cm3. In comparison, Earth’s density = 5.5 g/cm3, and water on Earth 1 gm/cm3. GJ1214b’s larger density suggests that it has more water and less solid material.

“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water’ – substances that are completely alien to our everyday experience,” Berta explains. Furthermore, GJ1214b cannot harbor any bodies of liquid water due its temperature and proximity to its parent star.

He and his colleagues utilized Hubble to measure GJ1214b’s light spectrum. The spectrum is apparently not restricted to any particular wavelengths, which indicates and further proves the state of the atmosphere. The team is also currently attempting to study the exoplanet’s sunsets through infrared using the Hubble; they can see through the atmosphere more easily with infrared than if they used visible light, which is shorter in wavelength and, hence, cannot traverse thick mediums readily.

According to CfA, theorists have predicted GJ1214b’s formation:

“GJ1214b formed farther out from its star, where water ice was plentiful, and migrated inward early in the system’s history. In the process, it would have passed through the star’s habitable zone. How long it lingered there is unknown.”

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