Exoplanet pairs may be masquerading as singles

New Scientist ^ | July 7, 2009 | Lisa Grossman

[SunkenCiv]

Of the 353 known planets outside the solar system, 227 were found by watching the movement of a star for signs of an orbiting planet's gravitational tug. This technique is known to sometimes miss sibling planets. Now a team at the University of Arizona, US has worked out that around half of those 227 may have a secret sibling... the effects of two planets with fairly circular orbits can combine to have the same effect on a star as one planet with a very eccentric orbit, says Timothy Rodigas, a graduate student at the University of Arizona. More than two planets can also combine to have this effect, although so far many more double-planet systems have been observed than with more than two. Rodigas and colleagues have developed a technique to estimate how many hidden siblings are out there, and where to look for them. The team used the masses and orbital parameters of the 227 supposedly single exoplanets to randomly generate a "zoo" of 10,000 fake exoplanets. A fraction of them were then randomly designated eccentric singletons, with the rest given circular orbits and each assigned a companion planet, also with a circular orbit. The final step was to calculate the effect each system would have on its star, and compare the results with the real measurements. The best match between the two is achieved when 45 per cent of the solar systems have at least two planets in relatively round orbits. Applying that proportion to the 227 observed exoplanets suggests more than 100 of them have a hidden sibling... Rodigas's analysis suggests that the best candidates for planets with hidden companions lie in an eccentricity sweet spot between 0.1 and 0.3 -- an orbit much like that of Mercury.

[SunkenCiv]

The effects of two planets with fairly circular orbits can combine to have the same effect on a star as one planet with a very elongated orbit, new research suggests (Illustration: ESA)

[SunkenCiv]

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[cripplecreek]

I would think they would have to orbit pretty close to each other to produce the effect. Otherwise the inner planet would be outrunning the outer planet.

[agere_contra]

Damn I must be tired. I assumed this was a thread about gay activists.

[SunkenCiv]

The transits are so brief, and odds so low that the stars are under observation at just the right time, that this method may not be that hot anyway. :') However, any exoplanet which resolves to a pretty wacky orbit probably is two (or more). :')

Gliese site:freerepublic.com

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[Psycho_Bunny]

This article is painting the issue in a way that makes it sound like astronomers JUST NOW figured out that there might be a problem with the detection method.

That is not the case.

[mikrofon]

Time for them to come out of the gravitational well, so to speak...

[TalonDJ]

The problem is how far away they are. Since we can’t observet them directly we can’t see if they have rings.