Kepler Mission Options

[Hungry4info]

Agreed, 1 in 40 isn't that bad. And that's just with a baseline of a few months. The number will surely improve.

[Syrinx]

http://news.stanford.edu/news/2011/march/l...ets-030811.html

The search for planets around other stars - a talk at Stanford

Natalie Batalha, a key scientist in the search for Earth-like planets orbiting distant stars, will talk about the quest Thursday evening as the speaker for the annual Bunyan Lecture, presented by the Stanford Astronomy Program. The 7:30 p.m. talk is free and open to the public.

[...]

The lecture, which is free and open to the public, is scheduled for Thursday, March 10, at 7:30 p.m. in Braun Auditorium, in the Mudd Chemistry Building, 333 Campus Drive.

I just found out about this lecture about an hour ago. I hope to attend, but will have to cancel my existing plans. Wish I had known about this a few days earlier! How did this lecture sneak past us?

[Syrinx]

The number will surely improve.

Their 1:40 number has predicted improvements and predicted future discoveries built in to it.

Still, if you had asked me three years ago if I'd like a 1:40 ratio, I'd have replied with an emphatic "Yes! Are you crazy?!!"

[vikingmars]

The number will surely improve.

Interesting contribution Hungry4Info and Syrinx. But, in France, thanks to Jacques Laskar's work at CNRS(*) who demonstrated that, thanks to our big Moon, the conditions on our homeworld seems to be very special indeed, we do NOT refer anymore to the words "Earth-like" or "Earth analog" when referring to those new discoveries, but to "Earth-sized" planets which is scientifically much more accurate. The French Press now also uses this term, not to give the Public falses hopes about the findings of new Earths. By looking to Jacques Laskar's conclusions, one may assume that the number for "Earth-like" worlds will surely be much lower, while the number of "Earth-sized" planets will surely grow in the near future.
(*) "Stabilization of the Earth s obliquity by the Moon, Nature, 361, 615-617, February 18, 1993."

[Syrinx]

I agree with your general thought. We need better terms. Everybody has their own, and what's worse sometimes the terms overlap with differing meanings.

But as per the paper under discussion these worlds are definitely more than just Earth-sized. They are in the habitable zone. The paper calls them Earth-analogs, but again you can call them anything you want. I prefer to call them Earth-like, but my "Earth-like" category is the first step on a 3-step ladder.

http://www.unmannedspaceflight.com/index.p...st&p=149307

I can't comment on a moon being a requirement for any category of Earth-likeness. Haven't read the paper.

[Gsnorgathon]

We could take a cue from the Kepler team: they've got planet candidates, we could have Earth candidates. Meaning, the available data meet all criteria for Earth-likeness, but we lack sufficient data to say if a planet's Earthlike. (Of course, "Earthlike" opens a huge can of worms that I'm not going to touch here except to note that by present-day standards, Earth hasn't been Earthlike for most of its existence. But we already knew that.)

Also of note: "the full 3.5 to 6 year Kepler data set". I like that 6, but it's the first I've heard of it. I hope we keep hearing more!

I'm going to be lazy here since I've got work I'm supposed to be doing, but 2.5% of what, exactly? Surely not Kepler's entire sample of stars - 2.5% of 150,000 would give us 3,750 "Earth analogs" (of which Kepler would actually see - what? 375? that's still huge)! The original mission docs said they expected 50 - 60, IIRC.

EDIT:

OK, in the paper itself, we have this: "We found that 2% of stars have an Earth in the HZ; this means 3000 of the 150,000 Kepler stars have an Earth. Of this 3000, about 1 in 250, or 12 will be edge-on, producing a transit. The Kepler data set
contains 4 Earth and super-Earth planets colder than 300 K. This means that as of Feb 2011 Kepler found 30% of the transiting Earths and super-Earths that it will eventually find after 3~4 years."

So they're actually saying that Kepler will find <12 Earth candidates (since they've got "4 Earth and super-Earth planets").

Thing is, I thought the incidence of transiting planets was more like 1%, whereas if I'm reading it right they're saying it's .4%.

[hendric]

We could just call them all "Venus-like" until proven otherwise. That will keep the media off of them!

[Syrinx]

Thing is, I thought the incidence of transiting planets was more like 1%, whereas if I'm reading it right they're saying it's .4%.

It's a function of stellar radius, planet radius, and orbital radius. For a giant Jupiter in a 0.1 AU orbit it'll be 10% (just guessing). For a tiny Earth 100 AU out it'll be just about 0%.

For an Earth-Sun relationship I'm remembering 0.5% but it very well could be 0.4%.

[vikingmars]

"...the first step on a 3-step ladder."
http://www.unmannedspaceflight.com/index.p...st&p=149307
I can't comment on a moon being a requirement for any category of Earth-likeness. Haven't read the paper.

Thanks Syrinx : I feel good on your "3-step" ladder. Now you would need a "B prime" step : the stabilization of the Earth s obliquity by... (you name it, but it's the Moon for our home planet), because, as Jacques Laskar discovered, it helped stabilize also our climate over long periods of time (to match your "C" criterion) and be "Earth-survivable" as you say. Mars had not such chance...

[Hungry4info]

A moon specificially isn't really needed. Planets in nearby (stable) orbits can assist in stabilising the obliquity as well. A paper on 55 Cancri found that it's planets could support an obliquity-stabilised planet in the HZ without the need for a moon. I'd have to find the paper, perhaps later. Furthermore, I'm not convinced the obliquity stabilisation is even a requirement for a planet being Earth-like. Is Myr-long climactic stability (on average, neglecting the kyr-long fluctuations) a requirement for a planet to be Earth-like? The deserts have to stay the deserts, the jungles have to stay the jungles?

[vikingmars]

We could just call them all "Venus-like" until proven otherwise

You made quite a good guess after all :
"...I think that the atmospheres of extrasolar Earth-like planets would be more like Mars or Venus than the Earth." (see article herebelow)
http://www.spacedaily.com/reports/Computer...pheres_999.html
"The analog in our solar system for the planets we have considered here is Venus." (see "What if Extrasolar Planets are Rocky ?" from LPSC XXIX) :
http://www.lpi.usra.edu/meetings/LPSC98/pdf/1409.pdf

[siravan]

It's a function of stellar radius, planet radius, and orbital radius.

To the first approximation, (upper bound on) the probability of transit is 2atan((R+r)/d)/pi, where R is stellar radius, r is planetary radius and d is orbital radius. For Earth, it calculates to 0.6%, but note that it includes some marginal transits which are practically undetectable, so the probability of transit detection is lower. For Jupiter, it is 0.12%.

[Greg Hullender]

Just noticed a new Manager's Update on March 8: http://www.kepler.arc.nasa.gov/news/mmu/in...&NewsID=109

New and improved data processing software, that ought to be able to work across multiple quarters. Apparently the old software could only work on one quarter's worth at a time. That explains a lot!

--Greg

[Greg Hullender]

Another Manager's update: http://www.kepler.arc.nasa.gov/news/mmu/in...&NewsID=110

Another safe-mode event, and they're still working on it. Does it seem like Kepler has more of these than other craft, or are they just better about reporting them?

--Greg

[Syrinx]

Kepler definitely has them more frequently. I believe it's due to hardware differences.

I hate to say something not true, but at one of the lectures here in the Bay Area I vaguely remember somebody claiming it is due to an old star tracker. Again, I'm not sure about that. What I do remember is thinking that if there was ever a Kepler 2 that it would be trivial to solve with modern hardware.