Major exoplanet announcement by ESO [ Gliese 581 e ]

from http://www.eso.org/public/events/press-evt/exoplanet_press.html
If you see the program (http://www.jenam2009.eu/default.asp?ContentID=1327) Michel Mayor speaks Tuesday morning. It seems the Swiss team has some hot news...

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ESO, the European Southern Observatory, will host two press events
during the European Week of Astronomy and Space Science (JENAM 2009)
that takes place at the University of Hertfordshire, UK. The two events
are scheduled for the morning of Tuesday 21 April 2009.


At 11:00 BST/12:00 CEST, a press conference will highlight a major
and truly unique discovery in the field of exoplanets, made possible
with ESO telescopes.

From 11:30 BST/12:30 CEST until 13:30 BST/14:30 CEST, a special
writer’s workshop will be dedicated to the future 42-metre European
Extremely Large Telescope, which will become “The World’s Biggest Eye
on the Sky”. Science writers will be updated by the key players on the
status of this amazing project, which has gained wide support in the
scientific community, and whose go-ahead for construction is expected
in 2010.

From the abstract listing on the 2nd link provided by exoplanet's post:

Tuesday 9:30 am
http://star.herts.ac.uk/ewass/abstracts.pdf

Statistical Properties of the Rich Population of Super-Earths - Results of the Harps Survey
M. Mayor (Geneva University)

Abstract:
In the last six years, at la Silla Observatory, we have carried out a systematic survey to search for planetary systems. The extreme sensitivity of the HARPS spectrograph has led to the detection of an impressive population of low-mass planets on close-in orbits. Already several statistical properties are emerging. First comparisons will be made between observed distributions and predictions from models of planetary formation.

If this turns out to be true, and if no one here objects, I'll likely merge this topic with the "Number of small planets discovered with HARPS?" thread.

I'm eagerly waiting...

However browsing the 340 pages pdf, I've found some interesting points. Just as "aperitive", I've noticed that CHEPS team has finally come up with an orbital solution for HD 191760, that star previously known to host two planets in close orbits. Now it seems that an only substellar object is orbiting the star with an orbital period of 505.57 days (a=1.35 AUs) and high orbital eccentricity (e=0.64). The object lies in brown dwarf regime. Indeed running a Systemic simulation, I've found a mass of 39.5 Jupiter masses and e=0.64, getting a chi square=0.43 and jiiter=NaN).

Gliese 581e: 1.9 MEarth.

http://www.eso.org/public/outreach/press-rel/pr-2009/pr-15-09.html

There seems to be a large and unoccupied region, right smack where the habitatable region is, between the third and fourth planets. Maybe room for a small planet...

Also I have a lay question, are the masses calculated strictly the mass of the planets likely orbiting the star or a possible combined mass of the planets and their potential moon(s)? Leading on from this queston, could the two possibilities be distinguished?

Well, well. Actually I was thinking about a fourth planet right in the habitable zone (0.11 AUs), but I can't complain at all. It's the lowest mass (and closest) planet detected so far.

And there's also a nice probability of transit too, isn't it?

So... GJ 581 e? Pretty neat. Nice low mass. =). So this planet... isn't... in the habitable zone? With GJ 581 c being at the inner edge, and d being at the outer edge, wouldn't e be in the habitable zone? Perhaps toward the inner edge? And with a low mass like that, wouldn't it be hard for it to have such a thick atmosphere as c?
Would it be safe to say that the prospects for habitability for GJ 581 e are better for c?

Gj 581 e is at the inner edge of Gj 581 b, the hot Neptune. It cannot be habitable

Neither would GJ 581 d. At periastron it just mildly reaches the habitable zone, whereas at apastron it's far away from it.

Ohh... for some odd reason, I guess I assumed it was between c and d.

From UniverseToday

Quote :

Michel Mayor, a well-known exoplanet researcher from the Geneva Observatory, announced the find today. The planet, “e,” in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist.

The Extrasolar Planet Encyclopaedia also claims d is now in the habitable zone.

Sirius_Alpha wrote:

The Extrasolar Planet Encyclopaedia also claims d is now in the habitable zone.

And I don't get why. Since planet "d" could even lay in habitable zone, but only at periastron. Neither at average orbital separation or at apastron.
Moreover too massive to be habitable. A deep ocean world? Likely. Like those inferred in this Nature paper

What source are you using for the orbit of d? I agree with you that the orbital parameters (given at the EPE) of d suggest it's too cold to be in the habitable zone, However if the orbit of d has been refined, as the news stories suggest, then it may well lie farther in. When additional planets are found in a planetary system, the fit for the RV data changes for the other planets. Have you found these refined parameters? Those at the Extrasolar Planets Encyclopaedia don't seem to have been updated, as the reference for the parametersof d come from "The HARPS search for southern extra-solar planets, XI. Super-Earths (5 and 8 M) in a 3-planet system" which does not include the fourth planet.

As far as transits are concerned, I remember that possibility was raised when c was announced. The MOST satellite was used to observe Gliese 581 and it was determined that the star is very stable, photometrically. No transits were found from c over the timespan covered (which, if I remember right, was a fairly decent amount of time). I don't know if MOST is sensitive enough to have detected the transit of an Earth-sized planet.

Edit:
I got an email form the exoplanet newsletter describing changes to d's orbit.

Quote :

A 1.9 Earth mass exoplanet (period 3 days)
has been detected around Gliese 581 (Mayor et al).

See
http://exoplanet.eu/planet.php?p1=Gl+581&p2=d
It is the lightest planet detected up to date around a main sequence star.
In addition, the planet Gliese 581 d has a revised period of 67 days,
bringing it in the habitable zone of the parent star.
Jean Schneider

Edit 2:
I wasn't able to access the paper before (lame computer) but now I can.
http://obswww.unige.ch/~udry/Gl581_preprint.pdf is the discovery paper.

The HARPS search for Southern Extra-Solar Planets XVII. An Earth-Mass Planet in the GJ 581 Planetary System

Abstract wrote:

The GJ 581 planetary system was already known to harbour three planets, including two presumably rocky planets which straddle its habitable zone. We report here the detection of an additional planet – GJ 581e – with a minimum mass of 1.9 M. With a period of 3.15 days, it is the innermost planet of the system and has a 5% transit probability. We also correct our previous confusion of the orbital period of GJ 581d (the outermost planet) with a one-year alias, thanks to an extended time span and many more measurements. The revised period is 66.8 days, and locates the semi-major axis inside the habitable zone of the low mass star. The dynamical stability of the 4-planet system imposes an upper bound on the orbital plane inclination. The planets cannot be more massive than approximately 1.6 times their minimum mass.

(emphasis mine)

Edit 3:
If i put everything into Celestia right, it would seem that from the surface of e, planet b would be around 3 times the apparent size of the moon in our sky. (give or take, depending on the radius of the planet, which I assume to be about that of Neptune).

Edit 4:
An interesting discussion regarding the habitability of d.
http://listes.obs.ujf-grenoble.fr/wws/arc/exoplanets/2009-04/msg00000.html
Seems that d isn't in the habitable zone after all.

Well that paper doesn't give the parameters of where the planets are in their orbits at a given time (e.g. time of periastron, or mean anomalies at a given time). How annoying.

This has hit the arXiv, with a nice surprise for orbital elements completists.