Faraway Planets Orbiting Distance Stars

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Smaller faraway planets...

Neptunians Beyond the Solar System

Neptunian exoplanet.
NASA artist imagines the newly discovered Neptune-sized extrasolar planet circling the red dwarf star Gliese 436. Here, the planet appears gaseous like Jupiter, with a cloudy atmosphere. However, astronomers don't know yet if the newly discovered smaller planets are gaseous like Jupiter, or rocky like Earth and Mars.  click to enlrage
Astronomers looking for faraway planets orbiting distant stars have found a new class of such objects beyond our Solar System.

Far smaller than exoplanets found earlier, these planets are about 10 to 20 times the size of Earth.

That makes them about as big as the known planet Neptune and, therefore, they are referred to as neptunian extrasolar planets.

Exoplanets discovered earlier are the size of the known gas-giant planet Jupiter. The Neptune-sized planets prove that planets the size of Jupiter aren't the only ones out there, according to the astronomers.

Other systems. Neptune, Jupiter and Earth are in our Solar System. The new small planets are in solar systems around the stars Gliese 436, 55 Cancri, and mu Arae.

One of the newly-discovered planets is near three other previously discovered exoplanets orbiting the star 55 Cancri. Together, they form the first-ever-known four-planet system beyond our own system.

The several discoveries were made by astronomers at the Carnegie Institute of Washington, University of California at Berkeley, University of Texas at Austin, University of Lisbon in Portugal, Marseille Astrophysics Laboratory in France, and University of Geneva in Switzerland.

Just How Massive Is That Planet?
Astronomers compare the planets in our Solar System with Earth. Rather than list a planet's mass in kilograms, they compare its mass to Earth's mass. For instance, let's say Earth's mass is 1 and the mass of Jupiter is 318, then Jupiter is 318 times more massive than Earth.
Planet Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto
Mass 0.055 0.88 1 0.107 317.8 95.2 14.48 17.2 0.005

Are they rocky? To date, nearly 140 extrasolar planets have been discovered. All of the earlier discoveries have been larger planets of the size of Jupiter.

Astronomers wonder if the newly discovered smaller planets are spheres of gas like Jupiter or hard look like Neptune with a heart of rock and ice surrounded by an atmosphere of hydrogen and helium.

Because they are smaller than Jupiter, it is possible they are made of rock and ice, rather than gas. Like Earth, they may have formed through gradual accumulation of rocky bodies. A planet the size of Neptune may not have enough mass to hold onto a lot of gas.

These planets stay close to their parent stars, whipping around them in a matter of days. How were they found? The discoveries were made using a technique called radial velocity, in which a planet's gravitational pull is detected by the wobble it causes in the parent star.

A star's movement, including any wobbling is calculated by measuring the Doppler effect on light arriving at Earth from the star. The wavelength of the star's light changes as it moves. That tells astronomers a lot about the star and objects near it, including mass, orbit and speed. Future searches. While astronomers will continue searching for extrasolar planets with the telescopes already in place, NASA is planning to launch even more specialized equipment seeking more Earth-like planets.

Three planet-hunting projects in the works are named Kepler, the Space Interferometry Mission (SIM), and the Terrestrial Planet Finder (TPF).

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