Physics Question #389

Eric Cashmore, a 13 year old male from the Internet asks on June 4, 1998,

What is the name of the most recent planet discovered, and where is it?

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The answer

Donald J. Barry answered on June 4, 1998

The object recently discovered with the Hubble Space Telescope, and which has been termed a planet by some, is in our own galaxy. The last few years have been an exciting time for planet-hunters, with almost ten objects now identified as strongly probable candidates. All of them are in our galaxy, since our largest telescopes are not yet capable of searching for the faint signatures of planets in the starlight of single stars in other galaxies.

None of the planets so far discovered have been named aside from being associated with the catalog identification of their parent stars. There is no tradition for assigning "popular" names to objects outside our solar system, with the exception that binary stars are still referred to with the name of the discoverer (i.e., Worley 3 would be the third binary or double star discovered by the astronomer Charles Worley).

In the astronomical community, naming is a complicated process which is overseen by the International Astronomical Union (IAU), a worldwide association of professional astronomers. At their triennial (once every three year) meetings, a special committee on naming meets to assign names to newly-discovered "nameable" objects (asteroids, craters, and the like), and to consider larger issues such as whether new rules on naming need to be made.

In the issue of this newly discovered object, though, I must express a little caution about whether it's a planet or not. Some astronomers feel it is a very lightweight star. It is difficult, with objects as young as this, to distinguish the two. Since it seems associated (via a trail of gas and dust) with parent stars, themselves recently born, it is quite young and therefore very hot. Whether nuclear reactions take place in its core or not (the hallmark of a star) is very difficult to determine from measurements of its surface. And critically, since it is a single object, it is very difficult to measure its weight.

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