The smallest "exoplanet" -- AMIGA Astronomy

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Subject: The smallest "exoplanet"

Author:
Cheungpui

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Date Posted: 13:40:54 02/14/05 Mon

Astronomers have discovered the smallest exoplanet.
The discovery is actually of a fourth planet orbiting a pulsar, named PSR B1257+12, some 1,500 light years away in the constellation Virgo. The new planet is orbiting inside a large cloud of hot, charged gas that surrounds the pulsar. The mass of the new planet is only one-fifth that of Pluto � or only a 30th of the mass of the moon.
The reason the astronomers can detect the planet is that its star � a pulsar � sends out very exact pulses of energy every time it spins. Most pulsars spin so reliably and quickly that they rival atomic clocks for their accuracy. As a result, when there are any planets tugging on a fine-tuned pulsar, you can easily see the wobble, even from the gravity of a very small planet.
As for what makes the new planet and the system to which it belongs so similar to our own � the distances at which the planets orbit. They are like a half-sized version of how our planets are set up around the sun.

The first three inner planets in the pulsar's system orbit at distances that are proportional to those of Mercury, Venus and Earth. The fourth planet has an orbit about six times larger than the third planet, putting it in the equivalent position of the asteroid belt between Jupiter and Mars.

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