Astronomers tend to get excited by pinpricks of light. And perhaps today they have more reason than usual to celebrate the pixels that Paul Kalas at the University of California, Berkeley, and pals have found in one of the Hubble Space Telescope’s images.
These pixels, they say, represent the first optical image of a planet orbiting another star. The star in question is Fomalhaut in the southern constellation of Piscis Austrinus and one of the brightest in the sky.
Kalas and co say the planet is about three times the mass of Jupiter orbiting at a rather distant 119 AU. By comparison, Neptune orbits at around 30 AU so this is going to be one cold body.
That’s impressive work that has had significant press coverage but let’s put it in perspective.
Last year, the infrared Spitzer Space Telescope photographed HD 189733b, a Jupiter-sized gaseous planet orbiting a yellow dwarf in the constellation of Vulpecula. It even produced a heat map of the surface showing, unsurprisingly, that the planet is warmer at the equator than at the poles. But the map of HD 189733b got almost no coverage. And images of various “hot Jupiters” have been around for perhaps a decade or so.
I guess Hubble just has a better PR team.
Ref: arxiv.org/abs/0811.1994: Optical Images of an Exosolar Planet 25 Light Years from Earth∗
As far as I can tell, HD 189733b has been mapped but not photographed. Being so close to its star, it would have been very hard to photograph it. Mapping has been done by IR spectroscopy and looking at the difference between the star signal and the (star+planet) signal during transits.
There *are* indeed other photos of exoplanets in the IR (see 2M1207b) , but the Hubble one is a historical landmark because:
– it is the first in visible light
– it is the first image by the starlight reflected from the planet, instead of the IR emission of the accreting, still hot planet.
So it is the first image of the sunshine reflected by a cold exoplanet. It is the kind of familiar image we have of *our system* planets. That’s why it is so jaw-dropping.
Hubble does have good PR, but also consider this: HD 189733b was discovered via the transit technique and never directly imaged as the Fomalhaut b exoplanet was (among others).
Some pretty complex techniques had to be used to infer the temperature map, whereas in this case (as devicerandom points out) it’s visible light bouncing off a cooler object.
You’ve missed the point. The temperature maps derived for previous exoplanets have been derived by subtracting the flux from the parent star to reveal the weak thermal radiation from the exoplanet. All data on exoplanets to date has been inferred from observations of the parent star – be it their detection via radial velocity shifts or transits or similar techniques. These are the first observations where the light from the planet is clearly separated from the light of its parent star, and paves the way for resolved imaging and spectroscopy of other planetary systems.
Oh, and no one has used “photographs” in professional astronomy for many years, but we do obtain images using sensitive electronic detectors from the gamma-ray to radio regimes of the e/m spectrum, as do all other fields of physics.
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