Three Planets, and a New Category

by Paul Gilster on April 21, 2006

Three new planets have just been announced, but contrary to expectations, the number of planetary detections has not been picking up in recent times. The peak rate was 34 planetary discoveries in 2002, with the years since showing about 25 planets per year. There are a number of reasons for the slowdown, among them the fact that readily detectible short-period planets for the most obvious candidate stars have already been detected, and it will take years for enough data to accumulate to snare the presumably numerous outer planets in these systems. Greg Laughlin’s Systemic site provides the details.

But we do have a nice set of three new worlds delivered to us courtesy of the radial velocity method, which remains the primary detection scheme as we tune up transit and microlensing searches. HD 224693 offers a 0.7 Jupiter mass world in a 27-day orbit and HD 33283 shows a Saturn-class world in an 18-day orbit. HD 86081 is the most intriguing; it seems to have a 1.5 Jupiter mass planet in a tight two-day orbit. That extremely short orbital period sets up a high 17 percent transit probability, but no evidence for a transit has yet been found by the California-Carnegie Planet Search Team.

Note this, too, about the HD 86081 planet: the Optical Gravitational Lensing Experiment has found three out of five observed transiting planets to be in this category, with an orbital period of two days or less. Coupled with this latest find and accounting for selection bias among the two detection methods, we seem to have identified a class of worlds that the California-Carnegie team calls ‘very hot Jupiters,’ an apparently rare class of exoplanet occurring perhaps an eighth to a tenth as often as the far more commonly observed ‘hot Jupiters’ in somewhat wider orbits.

The paper is Johnson, Marcy, Laughlin et al., “The N2K Consortium VI: Doppler Shifts Without Templates and Three New Short–Period Planets,” available here.

ljk April 25, 2006 at 14:26

Can someone explain to me how any planet, I don’t care
how big it is, can survive being so close to its star that its
orbit is only a day or two long? Why haven’t these worlds
been vaporized away a long time ago? Or are we actually
looking at someone on the star itself, such as an elongated
shape?

I wonder if we will one day discover a Ptolemaic system,
one where a star orbits a planet? Hey, a decade ago,
astronomers assumed all Jovian type worlds circled their
suns in orbits that took decades to complete, not days.

Administrator April 25, 2006 at 14:55

Boy is that a good question! One would suspect these ‘very hot Jupiters’ can’t possibly have a long lifetime, but maybe we’ll be able to make better deductions with a few more detections.

Timothy J Mayes March 24, 2007 at 15:28

For Example let a private group buy a small launch vehicle , and launch
a solar light sail propelled 200 kilogram payload to a star by sending it
on an escape trajectory : to fly close to the sun & maximize the photonic
thrust. If a light sail were to fly just 100,000 miles from the sun’s surface
and survive it can reach about 10% of light velocity. It it goes 1,000,000
miles from the sun it can reach about 1% of light velocity. But if it flies
9,000,000 miles from the sun it can reach only 1000 km/sec for example
. These figures apply to light sail with loading of 1 gram mass per sqaure meter of light sail area.
Tim

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