Human Journey

“Sex c” New Planet Discovered

OK. If this headline makes you cringe rather than snicker, just stop reading this post right now.

Good? Great. On to the news.


An artist’s impression of a Jupiter-like exoplanet.

—Image courtesy NASA/JPL-Caltech

Late last month astronomers at the California Institute of Technology announced the discovery of four new extrasolar planets, two each around the subgiant stars HD 200964 and 24 Sextanis.

The pair of exoplanets found around HD 200964 got top billing, because the planets’ “intimate dance is closer and tighter than any previously seen,” according to the Caltech press release.

What astronomers found is that, even though the two worlds are gas giant planets each more massive than Jupiter, they orbit within 32.5 million miles (52.3 million kilometers) of each other.

By contrast, Jupiter and Saturn are the closest-together gas giants in our solar system, and they’re never less than 330 million miles (531 million kilometers) apart.

“This new planet pair came in an unexpected package,” astronomer John Johnson (no, I am not making that up) was quoted as saying.

But it turns out the other pair of exoplanets may be even funnier, thanks to the formal naming conventions for planets found orbiting other stars.

The two worlds circling 24 Sextanis are also in a close embrace, keeping within about 70 million miles (112.6 million kilometers) of each other.

What the CalTech release fails to mention is that the planets have names: 24 Sex b and 24 Sex c.

While each world in our solar system bears an official name based on mythology, the basic rule for naming an exoplanet is to use the star’s name followed by a lower-case letter. The star itself is considered “a,” so the first planet found gets labelled with a “b,” and so on through the alphabet.


A direct picture of exoplanets HR8799b, c and d.

—Image courtesy NASA/JPL-Caltech/Palomar Observatory

Sometimes the star names get abbreviated in the catalogs, so 24 Sextanis (itself named for the constellation it lives in, Sextans) got cut short—and hilarity ensues.

Sometimes newer stars get named after the instruments or techniques used to find them, giving us exoplanets with names such as OGLE-TR-56b.

That’s thanks to the Optical Gravitational Lensing Experiment (OGLE), which was designed to study variability in starlight.

OGLE data have helped astronomers find planets via the so-called Doppler wobble, slight dips in starlight caused by a planet’s gravitational pull.

Of course, this system can also mean that exoplanet names get increasingly unwieldy—NGC 4349 No 127 b just doesn’t have the same ring as say, Uranus.

The issue has led some people to suggest we should formalize a naming convention for exoplanets based on mythology, although at 473 planets and counting, we could run out of Greco-Roman names real fast.

Still others have said to save the proper names for habitable, Earthlike worlds.

Astronomical naming can get contentious, as evidenced by recent debacles over several newfound Kuiper belt objects. But it does tend to make life easier for those of us who have to talk about exoplanets to the public on a regular basis.

So, what would you name an exoplanet?

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    Why stick with the Greco-Roman pantheons? Earth has an extraordinarily long list of mythologies to pull from for naming stellar objects outside the Sol system. Norse, Chinese, Aztec?

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