Kepler Mission Options

[Syrinx]

I searched for a scientific guide on what qualifies as Earth-like or Earth-twin. Didn't find anything. I performed some research and analysis tonight and put together my own guide. Let me know what you think.

First, I've expanded on the two Earth- categories. I've defined four categories.

Earth-like
Earth-similar
Earth-twin
Earth-survivable (this is a special category meaning "habitable")

Second, I've defined five criteria:

A) Mass
B) Radius
C) Mean surface temperature
D) Breathable atmosphere
E) Liquid water

To meet criteria A and/or B, a candidate planet must be within 50% of Earth's value for that particular criterion.

Me = 5.97 x 10^24 kg
Re = 6371 km

To meet criterion C, a candidate planet must be within 25% of Earth's mean surface temperature.

Temst = 287 K

Criteria D and E are boolean values.

A candidate planet matching any of
- 2 criteria is Earth-like,
- 3 or 4 criteria is Earth-similar,
- 5 criteria is Earth-twin.

In addition, a candidate planet matching criteria C, D, and E is defined as Earth-survivable. Meaning a human could survive indefinitely on the planet's surface without technological assistance. Note this does not imply criteria A and B are necessarily met. For example, a planet may may have a much lower mass and a much smaller radius but still may be survivable.

Using my guide, both Mars and Venus are Earth-like. Mars meets criteria B and C. Venus meets criteria A and B.

Kepler would be able to categorize planets as Earth-similar planets at best, although some of them may later be determined to be Earth-twins or Earth-survivable by other scientific means.

[mcaplinger]

I searched for a scientific guide on what qualifies as Earth-like or Earth-twin. Didn't find anything.

Astronomers can't even define a planet, much less an Earthlike one

Rather than "Earthlike" I might suggest "habitable" and start with the criteria in the classic "Habitable Planets for Man" by Stephen Dole, now available online http://www.rand.org/pubs/commercial_books/CB179-1/

[Holder of the Tw...]

For example, a planet may may have a much lower mass and a much smaller radius but still may be survivable.

We have no idea what the long term effects of low gravity on living organisms are, beyond two and a half years of lunar gravity on completely dormant microorganisms. Particularly if "survivable" means multi-generation sustainable.

[centsworth_II]

...Rather than "Earthlike" I might suggest "habitable"....[/url]

"Habitable for man" refers to a specific point in Earth's life. Life arose on this planet in very inhabitable circumstances from a human point of view. I'd think that Earth-like or Earth twin could refer to a planet that might resemble Earth at any point in its history.

edit: Perhaps you meant habitable by any life as we know it, not just human life.

[Syrinx]

mcaplinger:

In my guide, Earth-like in no way implies habitable. A planet may meet criteria A, B, and C but might have a toxic atmosphere, for example. "Habitable" may be a better description for the "Earth-survivable" category.

Also, thank you for the link to the book. I'll definitely pick that up.

Holder:

There are many ways we can define survivable, and it's literally impossible to do so accurately with so few criteria. I used the phrase "survive indefinitely" but obviously that's not realistic because it implies a ready food source. For now I'll agree that certain criteria may be missing out of need for simplicity.

After a few hours to think about it, I've decided to tweak a few points from my original definitions. I'll change the mass and radius criteria to a tolerance of 50%. Surface temperature will remain with a tolerance of 25%. Mars now qualifies as Earth-like based on radius and surface temperature. Venus remains Earth-like based on radius and mass. Editing original post now... check above.

[Syrinx]

"Habitable Planets for Man" by Stephen Dole, now available online http://www.rand.org/pubs/commercial_books/CB179-1/

I read through the PDF. Interesting read.

It's not entirely applicable, however. One problem is I'm looking for a guide that we can utilize with Kepler's discoveries, hence the Earth-like and -similar categories. Dole defines only the habitable (Earth-survivable) category.

For habitability, Dole's criteria are:

- temperature
- light (sunlight)
- gravity
- atmosphere
- water

Those match up pretty well with my five criteria. The differences being the addition of light and gravity, and the removal of radius and mass. My counterpoints to Dole:

- The sunlight criterion might shake out from the temperature, atmosphere, and water criteria. Both my guide and Dole's guide have temperature, atmosphere, and water.
- My guide sort of has gravity as well, but in the form of mass and radius. I like mass and radius over gravity because we can directly apply them to Kepler's discoveries and classify a planet as Earth-like. Whereas using gravity alone might require us to match the gravity criterion after discovering a super dense basketball.

[djellison]

I would ask people to refer back to the rules at this point - this discussion isn't really in the jurisdiction of UMSF, and is in danger of falling foul of several rules.

[Byran]

http://kepler.nasa.gov/about/manager.html

Kepler completed another science data download over October 18-19.

[Byran]

http://archive.stsci.edu/mast_news.php?out...sc=t&id=342

Unfortunately, public data (calibrating photometry for 10 days May 2009) there is no known transiting planets, or short period known variables.

Found only long period variable - U Lyr (Mira type)
http://simbad4.cfa.harvard.edu:8080/simbad...p;submit=submit



other star from public data Kepler
http://simbad4.cfa.harvard.edu:8080/simbad...p;submit=submit
not variable in Simbad



p-mode K-giant star?

[tacitus]

From the latest mission report

Random noise is present in all measurements and cannot be calibrated out. Therefore, strict requirements were placed on the design of Kepler’s spacecraft systems to limit random noise to a low level. Measurements taken in space confirm that Kepler meets its random noise requirements.

Systematic noise results from the imperfect nature of any measuring device. It represents the instrument’s “finger print” placed upon the measurement, and must be calibrated out of the data in post-processing on the ground. Because systematic noise depends on the specific characteristics of the instrument, the best calibration requires that the noise sources be characterized and modeled based on measurements made in space. The Kepler team has been developing the ground software to calibrate out the various systematic noise sources since launch, and this work will continue for a number of months. As each source of systematic noise is calibrated, fainter transit signals can be detected. Data collected from the spacecraft will be continually reprocessed as the ground software matures, revealing smaller and smaller planets. This is a normal process and has been part of the Kepler plan since before launch. Fortunately for Kepler, the worst sources of systematic noise affect only a small portion of the field of view, so the majority of the field of view will be calibrated earlier, enabling small planets to be detected sooner.

So we finally get it from the horse's mouth. It's still short on the specifics, but they are essentially telling us that:

i) The worst sources of noise are restricted to a small number of detectors.

ii) The raw data from Kepler can be processed and reprocessed as the sources of noise are characterized and countered. This holds true for the worst affected detectors though it will take more time to clean up those signals, and thus a delay in finding a minority of the detectable Earth-sized planets.

No doubt one can surmise that the noisier channels will never be made as clean as the better behaving channels, but they still seem to be implying that they will be able to squeeze Earth-sized planets out of all the data eventually.

It should help that the majority of transits with periods much shorter than a year will not fall on the same detectors so, for example, if one transit of a planet with a 3 month orbit hits a noisy detector, there will three other transits detected by low noise channels, thus the team will know where to look for a transit in the noisy data too. That should help calibrate and confirm their "noise abatement" algorithms as they proceed.

[imipak]

The words that stand out to this layperson, in the context of the news report, are

This is a normal process and has been part of the Kepler plan since before launch.

[Holder of the Tw...]

The third safing event, no science lost as this was just before a successful download.

[tacitus]

The third safing event, no science lost as this was just before a successful download.

I was initially worried that the safing events would create too many gaps in the data for transits to fall into, but I guess that the odds of them losing more than one instance of the same planetary transit are small, and should they discover that two other transit instances line up with one of the gaps in the data, they can infer that there likely was a transit during that time.

Not long now before the first full science results are released -- a couple of months away, or so.

[Ron Hobbs]

TIME is reporting that "[The Kepler team] has already submitted 28 scientific papers based on 43 days of data or less," says MIT planet theorist Sara Seager. "It's going to be a big year for planets."

Entire article here

I am getting pretty excited about the coming new year!

[MahFL]

That link does not seem to be about Kepler and 28 papers......