Hottest Ever Exoplanet Discovered: WASP-12b

Planets approximately the size of Jupiter orbiting close to their star in other systems are often referred to as “Hot Jupiters.” It would appear that a new classification is required: Very Hot and Very Fast Jupiters. WASP-12b is an exoplanet, about 50% more massive than Jupiter, orbiting a star (imaginatively called WASP-12) over 800 light years away, but it isn’t any ordinary exoplanet. It orbits its host star 1/40th of the distance at which the Earth orbits the Sun and it takes a breathtaking one day to complete one orbit. As a consequence, its host star heats WASP-12b to record-breaking temperatures; the planet is being toasted up to 2250 °C. For an exoplanet of this size, to be orbiting so close to a star has caused a stir amongst planet hunters. WASP-12b is and oddity, there’s nothing else like it… so far.

This new discovery originates from the UK’s Wide Area Search for Planets, a.k.a. “SuperWASP”. SuperWASP is a robotic system surveying both hemispheres, consisting of two observatories (one in the Canary Islands, off the coast of Africa, called SuperWASP-North; one in South Africa called SuperWASP-South) with eight cameras in both. The north and south observatories are on the look out for extrasolar planets, but rather than focusing on one star and seeing whether it wobbles (thereby giving away the presence of the gravitational pull of an orbiting planet), SuperWASP looks out for the periodic dimming of stars as their companion planets pass in front of them. Since it began operations in 2004, the two observatories have found 15 transiting exoplanets (as of April 2008).

Artist illustration of the planet orbiting the sun-like star HD 149026 (U.C. Santa Cruz)
Artist illustration of the planet orbiting the sun-like star HD 149026 (U.C. Santa Cruz)
Now, astronomers have focused their attentions on one rather strange exoplanet. When WASP-12b was first seen by the robotic planet spotters, researchers knew they were on to something special. The speed at which WASP-12b was transiting its host star (WASP-12) indicated that it had an orbital period of only 1.1 (Earth) days. This therefore meant that it had to be located very close to the star. This meant that it was going to be hot. Very, very hot in fact. Early estimates put WASP-12b’s surface temperature into the record-breaking range, possibly challenging the calculated temperature of HD 149026b, an exoplanet some 257 light-years away in the constellation of Hercules, with an estimated temperature of 2050°C. WASP-12b has an estimated surface temperature of 2250°C – that’s half as hot as the temperature of our Sun’s photosphere, and approximately the same temperature as many Class M stars.

Although impressive, there may be hotter “Hot Jupiters” out there, but the orbital velocity of WASP-12b will be a tougher record to beat. To date, most Jupiter-sized exoplanets have orbital periods of a few days, which led astronomers to believe there was some planetary mechanism preventing these planets from migrating very close to their host stars. Although Jupiter-like planets will have formed further away from their stars, they drift closer as they evolve until they settle into a stable orbit. Usually these orbits are located far away from the star, but WASP-12b obviously didn’t read the rule book before it set up home in its stellar oven.

When the planets form and migrate inward, something is causing them to stop and preferentially stop with a period of three days,” said Leslie Hebb of the University of St Andrews, UK. “I was surprised that the period could be so much shorter.”

So WASP-12b has a strange orbit, making it orbit very fast, causing it to be heated to astounding temperatures. But the strangeness doesn’t stop there. It has a diameter 1.8 times that of Jupiter, far bigger than gas giants are thought to grow. However, the extreme temperatures WASP-12b is experiencing may explain its obesity problem – the star could be causing the planet to “puff up,” making the gas giant less dense, but blowing it 80% larger than Jupiter proportions.

Now, SuperWASP researchers hope to probe the planetary system for UV light radiating from the exoplanet, possibly showing evidence that WASP-12b’s atmosphere is undergoing aggressive stripping or evaporation at such close proximity to the host star.

Source: New Scientist

19 Replies to “Hottest Ever Exoplanet Discovered: WASP-12b”

  1. Can someone clear my doubts? We need house plans when building houses, we need drawings when buidling bridges. What can the Artist Illustration help us?

  2. Being that close I wonder if it would cause “tides on the surface of the sun” if so how cool is that

  3. I wonder if the planet is distorted due to tidal forces as well.

    Also, are they sure that the orbit is stable? At some point, when one of these planets gets close enough, it should spiral into the star.

    That would be a spectacular event!

  4. Could this be yet another huge sunspot mistaken for a planet? It has been spotted via the transit method, has this been verified with the wobble method? And lastly, could this planet be in an elliptical orbit seen only at perihelion?

  5. I’ll second that doubt. Can the researchers positively eliminate a sunspot-like structure? I recall a previous article in which a star was reported to be hugely asymmetrical in its brightness, which was presumed to be a very large sunspot analog.

  6. @rob b – ‘tides on the surface of the sun’ – cool thought. along the same lines, would the proximity of the planet mean the star will literally the strip the planet to nothing over time? isn’t a large jupiter simply a big ball of gas?

  7. @ robbb
    I would guess that if it’s that close and has been there for any length of time it must have a wicked magnetosphere. Other wise it presumably would lose a lot of mass to solar wind. All in all not a good place to live

  8. I think what we are going to move towards, is a rocky planet is more than 60% formed before a star lights up. Which means planets are in a bath of gas and dust. When the star lights up and begins to clear out the area around itself, planets hold onto this gas. Bodies without much mass will eventually lose the ability to hold onto the gas.
    To me, this is a much more likely reason the Earth has so much water, and it is likely Mars did as well, however it just doesn’t quite have enough mass to hold onto its atmosphere.

    Even now, the concensus is the large gas planets have rocky cores slightly larger than Earth. They were able to achieve even greater mass with the availability of ice/frozen matter, and a longer period of time before the solar winds cleared those areas. Allowing them to have much greater atmospheres than Earth, and continue to build mass until the solar system was cleared out by the solar winds.

    With this in mind, I’m not at all shocked with the amount of “hot jupiters” we are finding.

    Thankfully, the future holds quite a few projects which will increase our imaging capabilities of stellar nurseries, and within 20 years I believe we will have a very good understanding how our solar system evolved.

  9. “Mmmm, is this going to make [gravity] waves? Can we detect them?”

    Yes they’d be produced (as would Earth and the Sun, or any other two bodies orbiting each other), but they’d be insanely weak, even as gravity waves go, carrying away insignifigant energy over all but the very longest time frames.

    Your best bets for gravity wave detection involve much more massive objects, moving much faster around each other. A close pair of neutron stars or stellar black holes, for example.

  10. Questions to the specialists:

    – do you know whether there is a model to predict how “our system”, which we know contains a Earth-like, life harbouring planet — would be detected using the current instrumentation from let us say 10ly, 80ly, 100ly, 200ly, …?

    – if such model does not existi, what does it take to put it together (for numeric analysis) considering different visualisation angles, distances, etc?

    – what else could be learned and detected from this model? e.g. presence of multiple sub-Jovian planets, presence of life-related chemical elements, etc?

    It would be great to hear your throughts on that!! Please, email directly if I can contribute with teh data model and/or computer simulation!


    F Koch

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