Esa | Major Scientific Discovery, At the 25th we'll know Options

[Guest_paulanderson_*]

NSF press release is now online:

http://www.nsf.gov/news/news_summ.jsp?cntn_id=105759

More post-press briefing info also:

http://www.nsf.gov/news/newsmedia/planet06

[Betelgeuze]

I couldnt resist:

[ljk4-1]

Paper: astro-ph/0601486

Date: Fri, 20 Jan 2006 20:51:31 GMT (149kb)

Title: Rapid Formation of Gas Giant Planets around M Dwarf Stars

Authors: Alan P. Boss

Comments: 22 pages, 8 figures, 1 table. ApJ, accepted
\\
Extrasolar planet surveys have begun to detect gas giant planets in orbit
around M dwarf stars. While the frequency of gas giant planets around M dwarfs
so far appears to be lower than that around G dwarfs, it is clearly not zero.
Previous work has shown that the core accretion mechanism does not seem to be
able to form gas giant planets around M dwarfs, because the time required for
core formation scales with the orbital period, which lengthens for lower mass
stars, resulting in failed (gas-poor) cores unless the gaseous protoplanetary
disk survives for > 10 Myr. Disk instability, on the other hand, is rapid
enough (~ 1000 yrs) that it should be able to form gas giant protoplanets
around even low mass stars well before the gaseous disk disappears. A new suite
of three dimensional radiative, gravitational hydrodynamical models is
presented that calculates the evolution of initially marginally gravitationally
unstable disks with masses of 0.021 to 0.065 solar masses orbiting around stars
with masses of 0.1 and 0.5 solar masses, respectively. The models show that gas
giant planets are indeed likely to form by the disk instability mechanism in
orbit around M dwarf stars, the opposite of the prediction for formation by the
core accretion mechanism. This difference offers another observational test for
discriminating between these two theoretical end members for giant planet
formation. Ongoing and future extrasolar planet searches around M dwarfs by
spectroscopy, microlensing, photometry, and astrometry offer the opportunity to
help decide between the dominance of the two mechanisms.

\\ ( http://arXiv.org/abs/astro-ph/0601486 , 149kb)


Paper: astro-ph/0601278

Date: Thu, 12 Jan 2006 23:44:50 GMT (190kb)

Title: On the Formation of Gas Giant Planets on Wide Orbits

Authors: Alan P. Boss

Comments: 13 pages, 4 figures. in press, ApJ Letters
\\
A new suite of three dimensional radiative, gravitational hydrodynamical
models is used to show that gas giant planets are unlikely to form by the disk
instability mechanism at distances of ~100 AU to ~200 AU from young stars. A
similar result seems to hold for the core accretion mechanism. These results
appear to be consistent with the paucity of detections of gas giant planets on
wide orbits by infrared imaging surveys, and also imply that if the object
orbiting GQ Lupus is a gas giant planet, it most likely did not form at a
separation of ~100 AU. Instead, a wide planet around GQ Lup must have undergone
a close encounter with a third body that tossed the planet outward to its
present distance from its protostar. If it exists, the third body may be
detectable by NASA's Space Interferometry Mission.

\\ ( http://arXiv.org/abs/astro-ph/0601278 , 190kb)

[Jyril]

I wonder if this planet could be warm enough to be a hypothetical ocean planet. See this link: http://corot.oamp.fr/pub/Ocean_planets.pdf.

[Jyril]

I feel uncomfortable about their claim that this discovery somehow increases the ratio of small planets to giants, simply because they have found only 2-3 giants vs the 15 or so expected before finding a small planet.  One point does not make a statistical argument.  They need at least 3 small planet finds to really say they have some proof of a ratio.

Indeed, they're really bold to make that claim. However, radial velocity searches have been rather unsuccessful finding massive Jovian planets around red dwarfs. Only two are known, and both orbit Gliese 876. Despite that, 3 of 8 least massive planets (not counting this one!) orbit a red dwarf. So, it appears low mass planets are more common around red dwarfs. At least compared to massive planets.

[SigurRosFan]

I could't resist, too.

Enjoy ...

The hot one and the cool snowball:

[Guest_Richard Trigaux_*]

Next steps should be:


-coronograph observation of the planet, to try to have some more orbit info (we have just a distance at a moment, not an orbit). But at 22000 light years, I don't know what is possible. Even much closer and larger planets are not observable today. On the other hand, the ratio star luminosity versus planet luminosity is much better for a red dwarf star.

-Spectrum of the planet (same remark as previous)

-MACHO search for new positions of the planet in front of background stars


-SETI search, although there is little chance that such a planet hosts a technology civilization.

[Guest_Richard Trigaux_*]

I wonder if this planet could be warm enough to be a hypothetical ocean planet. See this link: http://corot.oamp.fr/pub/Ocean_planets.pdf.

The temperature indicated is that of the surface, eventually top of clouds, and it is a calculated temperature, not measured. The ground temperature depends on the thickness of the atmosphere, and it could be anything between -250°C (if there is no atmosphere) and thousands of degrees (if there is a large mass of hydrogen, like on Uranus which has 15% of its mass in hydrogen, and is only 3 times larger than OGLE).

The second parametre is the quantity of water available, which can be zero (no atmosphere) to thousands of kilometres thick. Intermediates can be many: small lakes, ice caps, ice layer, icy planet, dry planet with water sequestered in high atmosphere like on Venus, ocean covered with ice like on Europa, free ocean with or without continents...

[ljk4-1]

Paper: astro-ph/0601563

Date: Wed, 25 Jan 2006 01:39:42 GMT (541kb)

Title: Discovery of a Cool Planet of 5.5 Earth Masses Through Gravitational
Microlensing

Authors: J.-P. Beaulieu, D.P. Bennett, P. Fouque, A. Williams, M. Dominik, U.G.
Jorgensen, D. Kubas, A. Cassan, C. Coutures, J. Greenhill, K. Hill, J.
Menzies, P.D. Sackett, M. Albrow, S. Brillant, J.A.R. Caldwell, J.J. Calitz,
K.H. Cook, E. Corrales, M. Desort, S. Dieters, D. Dominis, J. Donatowicz, M.
Hoffman, S. Kane, J.-B. Marquette, R. Martin, P. Meintjes, K. Pollard, K.
Sahu, C. Vinter, J. Wambsganss, K. Woller, K. Horne, I. Steele, D. Bramich,
M. Burgdorf, C. Snodgrass, M. Bode (PLANET) A. Udalski, M. Szymanski, M.
Kubiak, T. Wieckowski, G. Pietrzynski, I. Soszynski, O. Szewczyk, L.
Wyrzykowski, B. Paczynski (OGLE), and the MOA Collaboration
\\
In the favoured core-accretion model of formation of planetary systems, solid
planetesimals accumulate to build up planetary cores, which then accrete
nebular gas if they are sufficiently massive. Around M-dwarf stars (the most
common stars in our Galaxy), this model favours the formation of Earth-mass to
Neptune-mass planets with orbital radii of 1 to 10 astronomical units (AU),
which is consistent with the small number of gas giant planets known to orbit
M-dwarf host stars. More than 170 extrasolar planets have been discovered with
a wide range of masses and orbital periods, but planets of Neptune's mass or
less have not hitherto been detected at separations of more than 0.15 AU from
normal stars. Here we report the discovery of a 5.5 (+5.5/-2.7) M_earth
planetary companion at a separation of 2.6 (+1.5/-0.6) AU from a 0.22
(+0.21/-0.11) M_solar M-dwarf star. (We propose to name it OGLE-2005-BLG-390Lb,
indicating a planetary mass companion to the lens star of the microlensing
event.) The mass is lower than that of GJ876d, although the error bars overlap.
Our detection suggests that such cool, sub-Neptune-mass planets may be more
common than gas giant planets, as predicted by the core accretion theory.

\\ ( http://arXiv.org/abs/astro-ph/0601563 , 541kb)

[odave]

[exoplanet spectra]...I can't remember its alpha-numeric designation right now...

Here's a followup - I was thinking of the transiting "hot Jupiter" HD 209458b. It's featured in the article "Unveiling Distant Worlds" by Sara Seager in the February 2006 issue of S&T. The article covers the starlight subtraction method used to examine this exoplanet's atmosphere - sodium and atomic hydrogen were detected using HST. Spitzer was used to detect IR photons directly from HD 209458b by taking advantage of the "secondary eclipse", which happens when the planet passes behind its star. From the Spitzer data, they were able to get a temperature measurement of 1130K for the planet. It was an interesting read.

[Bob Shaw]

I liked the Space Daily strapline: 'Small planet found orbiting ordinary star'!

At last, an end to hype...

Bob Shaw

[dvandorn]

Reminds me, in a sort of strange way, of a headline in my hometown newspaper from 40 or 50 years ago.

I grew up in Bloomington/Normal, Illinois -- a "twin cities" set of mid-sized towns that had started out about 6 miles apart but had grown together over the course of many years. I was actually born and raised in Normal (leading me to tell people that I started out Normal, but have been moving farther and farther away from Normal ever since.)

There are any number of small farming communities surrounding Bloomington/Normal, and some of them have rather, well, odd names. One of these small towns is Oblong, Illinois. (You can look it up on maps. The place really exists.)

So (as I indulge my passion for making a short story ever longer... hehehehe...), the Bloomington Daily Pantagraph once ran a headline in their wedding announcements column that read:

Normal Man Marries Oblong Woman

It's the complete truth, I swear...

-the other Doug

[ljk4-1]

LOW-MASS EXOPLANET

Three international groups have teamed up to discover what is probably the
lowest-mass planet ever found around a normal star. The planet's mass is
between 3 and 11 times that of Earth, with a most likely mass of 5.5
Earths. The previous record-holder, which orbits the red-dwarf star Gliese
876, contains about 7.5 Earth masses. The only known exoplanets with lower
masses are four objects orbiting a pulsar -- the collapsed core of a
massive star that went supernova....

http://SkyandTelescope.com/news/article_1667_1.asp

[ljk4-1]

NEW KID ON THE GALACTIC BLOCK (Science Show: 28/01/2006)

A truly global cooperative effort was involved in the discovery of a new
planet in our galaxy, which is the closest thing to Earth ever found outside
our solar system. The planet, which has been named 'OGLE-2005-BLG-390Lb',
was identified by astronomers in 12 countries. Dr John Greenhill, one of the
Australian contingent, describes the latest find, which is located in the
constellation of Sagittarius, 22,000 light years away.

http://www.abc.net.au/rn/science/ss/stories/s1553310.htm

[ljk4-1]

Science/Astronomy:

* The Holy Grail: Small, Rocky Worlds

http://www.space.com/searchforlife/seti_sh...ail_060202.html

Normally, when astronomers trumpet the discovery of yet another extrasolar
planet, it's nearly always a hulking, Homeric object; Jupiter-sized or so.
However, the holy grail of the planet sleuths has been to find the small guys;
after all, bantam worlds are more likely to be similar to our own.