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Geek Trivia: Hot to spot

What's the hottest planet ever discovered, and what is its estimated surface temperature?

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It was a press release so geekishly profound as to make one suspect that the international community of astronomers had engaged in a massive April Fools' Day prank: On April 1, word broke that interstellar telescopes had finally managed to snap a visible photograph of a planet outside our solar system. Despite the instinct to disbelieve—astronomers have previously detected roughly 150 planets outside our solar system but confirmed none with photographs—the first glamour shot of an extrasolar planet is for real.

Orbiting the star GQ Lupi, the extrasolar planet has all the ingredients to make it easy to detect. First of all, this planet is big, with initial estimates placing it at one to two times as massive as Jupiter. Second, the planet is hot, with an estimated surface temperature of 3,140 degrees Fahrenheit (1,727 degrees Celsius).

Third, the planet orbits at a sizable distance from GQ Lupi—about 15 billion kilometers (9.3 billion miles). That's about 100 times the Earth's distance from our own sun and about three times Neptune's distance from the sun.

Finally, relatively speaking, GQ Lupi is not all that distant from Earth, residing in a star-forming region a mere 400 light-years from our solar system. Collectively, this paints the picture of a large, hot planet somewhat near Earth but far enough from its own sun to be visible in the solar glare.

But if that sounds too good to be true, it just might be. Researchers were well aware of the GQ Lupi planet before the photograph, having detected it via the traditional method—observing its parent star for a "wobble" caused by the planet's gravity—in 1999.

Some analytical models of that wobble suggest that the "planet" may be orders of magnitude heavier than Jupiter. That might push it over the controversial line separating mere gas giant planets and failed stars known as brown dwarves. If the object orbiting GQ Lupi is, in fact, a failed companion star, that could also explain its uncommonly hot surface temperature.

For now, however, scientists are classifying the GQ Lupi companion as a very distant, very hot planet. Yet, for all its unusual heat, the GQ Lupi planet doesn't even come close to qualifying as the hottest planet ever observed by science.


What's the hottest planet science has observed, a celestial object with a surface temperature that far surpasses the newly photographed GQ Lupi planet's more than 3,000-degree estimated surface temperature?

The current record-holder for the hottest planet known to science is HD209458b, and it boasts a searing surface temperature of 18,000 degrees Fahrenheit (10,000 degrees Celsius). The secret behind this scorching heat is the planet's startling proximity to its parent star—a mere 7 million kilometers (4.4 million miles)—which is closer than Mercury is to our own sun.

While this alone is extraordinary, you haven't heard the best part: HD209458b is nearly a third more massive than Jupiter. If you're wondering how a planet that's almost certainly a gas giant can survive so close to a star, the answer is it can't! HD209458b is "bleeding" hydrogen at a phenomenal pace—10,000 tons per second—literally shrinking as its mass tears away.

While scientists don't completely understand the exact process by which the planet is shrinking, current thinking suggests that a combination of solar wind, solar heat, and solar gravity are collectively boiling and tearing the planet apart, leaving behind a comet-like tail of shorn hydrogen as HD209458b orbits its parent star. Moreover, the rate of loss is likely accelerating, though science has yet to precisely pin down the rate of increase.

By the time the shearing process is complete, the planet will be stripped to its core, which will likely be a molten or solid ultramass that caused the improbable gas giant to form in the first place. While scientists have seen binary companion stars form in such proximity, this so-called "hot Jupiter" star-and-planet pairing is unique, and its unusual arrangement has astronomers salivating over potential astrophysical discoveries.

HD209458b's year is only 3.5 Earth-days long, which allows astronomers to observe the planet transiting its parent star (HD209458, 150 light-years from Earth and visible with binoculars inside the constellation Pegasus) twice a week. This opens up an incredible range of observational opportunities, which should make for great science—and some pretty good Geek Trivia.

The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best post from the assembled masses and discuss it in the next edition of Geek Trivia.

This week's quibble comes from the March 30 edition of Geek Trivia, "Pitching a perfect game(show)." Several readers questioned the suggested maximum cash winnings from a one-day appearance on the game show Jeopardy! In response, TechRepublic member Johngalt went so far as to break down the calculations for us.

"Round #1
"Six questions at $1,000 [=] $6,000
"Six [at] $800 [=] $4,800
"Six [at] $600[=] $3,600
"Six [at] $400 [=] $2,400
"Five [at] $200 [=] $1,000
"Total [=] $17,800
"Daily Double [=] $35,600

"Round #2
"Six [at] questions at $2,000 [=] $12,000
"Six [at] $1,600 [=] $9,600
"Six [at] $1,200 [=] $7,200
"Six [at] $800 [=] $4,800
"Four [at] $400 [=] $1,600
"Total [=] $35,200
"First Daily Double [=] $141,600 ($35,200 + $35,600 [x] 2)
"Second Daily Double [=] $283,200

"Final Jeopardy [=] $566,400
"The total given in the article is correct."

Thanks for watching my mathematic back, dear reader, and keep those quibbles coming.

For more, check out the Geek Trivia Archive.

The Trivia Geek, also known as Jay Garmon, is a former advertising copywriter and Web developer who's duped TechRepublic into underwriting his affinity for movies, sci-fi, comic books, technology, and all things geekish or subcultural.


Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger -- amusing and abusing IT pros. Read his full profile. You can a...