Off World

Astronomers Reel in a Haul of Five New “Hot Jupiters”

The Star-Huggers

When astronomers finally detected extrasolar planets in the 1990s, the earliest worlds they found were decidedly unlike anything in our solar system.

The first planets discovered were small, terrestrial-mass objects orbiting a pulsar—the ultradense, burned-out ember of a supernova explosion, which is famous for emitting phenomenal quantities of hard radiations.

Nothing Earth-like there.  Certainly not hospitable to life as we know it.

The second planetary system discovered was also unexpectedly alien—called 51 Pegasi b (subsequently christened “Dimidium”), it was a large, gas giant-type planet that circled a sun-like star, but in a much closer orbit than Mercury’s.  In fact, it completed a revolution in about 4 days.

It was only the first of what have come to be called “hot Jupiters”—large gas giants that orbit their primaries so closely they’re practically kissing the stellar photosphere.  They’re more common than you might think, and they lend themselves especially well to easy detection: they exert a powerful gravitational influence on their star, producing a noticeable “wobble,” and they create easily detectable eclipses when they transit their primaries.

And now an international team of astronomers has added five new members to the catalogue of “hot Jupiters.”  The planets were found using the Wide Angle Search for Planets-South (WASP-South) telescope-and-camera array in South Africa.  The discoveries were confirmed using photometric and spectroscopic instruments at the La Silla Observatory in Chile.

The discovery was published online on February 4 in the arXiv journal.

A "hot Jupiter" type planet circling a Sun-like star. Credit: Futurism M.A
A “hot Jupiter” type planet circling a Sun-like star. Credit: Futurism M.A
A Swarm of WASPs

The newfound planets have been christened—with an astronomer’s typical lack of imagination—WASP-119 b, WASP-124 b, WASP-126 b, WASP-129 b and WASP-133 b.  But concealed behind that unappealing string of alphanumerics is a whole universe of extraterrestrial strangeness.

For example, the first planet in the sample, WASP-119 b, is about 20% more massive than Jupiter, 30% larger, and whirls about its primary in only two and a half days.  Located about 1,000 light years away, the parent star is about the same mass as the Sun, but much older (about 8 billion years old).  The second planet in the sample, WASP-124 b, is about 1400 light years away, and about half the mass of Jupiter, but its primary is much younger than the Sun—only two or so billion years old.

Which indicates that the presence of a “hot Jupiter” is not a function of a star’s age—both the very old and the very young may possess them.

The third planet, WASP-126 b, seems to be the most interesting of the five.  It’s a little over 700 light years away, orbits a star almost exactly like our own (though about 2 billion years older), and is the lightest of the five planets—only about as massive as Saturn, but almost equal to Jupiter in size.  Which makes for easily the lowest surface gravity of the newly discovered planets.

Its parent star is also the brightest in the sample, so, according to Coel Hellier, one of the new paper’s coauthors, “This means it can be a target for atmospheric characterization, deducing the composition and nature of the atmosphere from detailed study, for example with the Hubble Space Telescope or the forthcoming James Webb Space Telescope.”

The final two planets, WASP-129 b and WASP-133 b, are 800 and 1700 light years distant respectively.  WASP-129 b seems to have the greatest surface gravity and longest orbital period (5.7 days) of the sample; WASP-133 b has the shortest period, at only 2.2 days.

Each new discovery of an extrasolar planet—no matter how alien and strange, no matter how ordinary and unremarkable—expands our understanding of that wild zoo of weird worlds circling other suns, and hopefully brings us a step closer to finding that first life-bearing exoplanet.

Planetary surveys such as that being conducted by WASP-South will continue to do its part, together with space-based telescopes like NASA’s Kepler and the future Transiting Exoplanet Survey Satellite.

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