Proxima Centauri, the hunt for planets.

Toward detection of terrestrial planets in the habitable zone of our closest neighbor: Proxima Centauri

For circular orbits:

Planets with m*sin(i) > 16 Earth masses ruled out within 1 AU.
Planets with m*sin(i) > 8.5 Earth masses ruled out with periods <100 days.
Planets with m*sin(i) > 2-3 Earth masses ruled out in HZ.

At first, I was surprised how stringent that was.
"2-3 Earth msses ruled out in HZ"
... then I realised the HZ is within arms reach of the chromosphere.

Still, not bad. It would be interesting to compare the limits as they've changed over time as our radial velocity surveying has gotten more accurate.

Not a discovery. More a planetological model...

Hmmm well it is still news (note the forum is "Extrasolar News and Discoveries" not "Extrasolar Discoveries")

It definitely doesn't fit in with "planetology" because this isn't really about properties of planets, but properties of the system, which is at odds with the description of the "Extrasolar Planetology" forum.

I was considering putting this in "Detection methods and projects" but wasn't entirely sure it fit well there either.

Just a suggestion. However nothing solid at the moment. Sadly

Also remember these are limits on m*sin(i). If Proxima has massive planets but their orbits are oriented face-on (small i), they wouldn't get detected by this method.

What are the prospects for the astrometric detection of planets around Proxima Centauri with small i?

Pale Red Dot Campaign
https://palereddot.org/

Apparently there is evidence for a planet at Proxima Centauri, but they want to confirm with HARPS observations. The public is invited to "follow" the campaign over two months. To verify that it's not magnetic activity, photometric observations from around the world will be taken simultaneously. Observations between Jan and April 2016.

Hmm. This is a surprise. I imagine the HARPS team are trying for a less secretive format due to the mess with Alpha Centauri B, which is probably a good thing. I also suspect that the ESO PR folks jumped on the occasion and made all of this stuff; which is, again, probably a good thing.

There isn't much of scientific value on the site right now, but I'm interested in seeing how far the parties are willing to share information like this.

(If I know anything about the HARPS team, they're going to be observing Proxima many, many hours a night this season, so expect a gigantic set of spectra! drools)

So I asked on Pale Red Dot's Facebook page and they confirmed that they have tentative evidence of a m sin i ~ 1-2 Earth-masses in the classical habitable zone of the star.

Quote :

...if it exists at all, the bulk properties are consistent with Earth-like (msin i ~1-2 MEarth and sits where you could comfortably enjoy a bath in a lake ...

Using some approximations, that implies an orbital period of ~4.9-5.0 days, not accounting for greenhousing (which would increase the period some). The RV semi-amplitude should then be ~2-3 m/s, which can't be better than ~twice the errors on a target like Proxima.

Something interesting I noticed while going through relevant literature:

Quote :

Concerning possible signals, the HARPS-TERRA RVs periodogram show a very marginal peak at 5.6 days that is also barely visible in the CCF values when the outlying RV measurement is removed.

(Anglada-Escudé & Butler (2012), which happens to be the paper that introduced me to the HARPS archive)

This is probably worth noting, though as that is based on a greatly reduced dataset, this may be coincidental. On the other hand, it may be the same signal, or perhaps an alias.

Though there is more data available on the archive now, it appears to be missing the 2014 season (though it would be proprietary), which would presumably be the most important one. I would wait until some more information is revealed before doing the thing.

What surprises me is that many teams, including that of HARPS, have already watched Proxima Centauri, without results apparently; What is the improvement of HARPS that will make the difference? Still is that it's well exciting

Led_Zep wrote:

What surprises me is that many teams, including that of HARPS, have already watched Proxima Centauri, without results apparently; What is the improvement of HARPS that will make the difference? Still is that it's well exciting

I felt they were rather clear about this. The data they have currently suggests the presence of a low-mass planet in the classical habitable zone, but they can't distinguish between a planetary cause or a magnetic cause. To do this, they either need to go back in time and collect photometric data on the star during the relevant observations, or collect new RV data simultaneously with photometry. The latter is what they chose to do.

Proxima's bolometric luminosity is ~0.0017 solar. Mass is 0.123 solar. Thus an Earth equivalent insolation is an orbit at 0.041 AU from Proxima with a period of 8.7 days. If the habitable zone for an Earth-like planet (rather than a massive CO2 greenhouse planet) is in the range of 0.8 AU - 1.2 AU in our solar system, then the orbital period range is 6.2 - 11.5 days.

Maybe the Pale Red Dot campaign for Proxima Centauri should be split out of the Alpha Centauri thread?

Anyway, they've apparently got half of their Doppler measurements for Proxima Centauri.

Latest update on the Pale Red Dot Twitter feed:

Quote :

Analysis of #palereddot data has been long and intense. A few things to polish here but conclusions look convincing... at least to us!

Hopefully getting close to the result (either positive or negative) being announced...

... and two other twits :



Submit to a scientific journal = real discovery ? (I think yes)

Quote :

Submit to a scientific journal = real discovery ? (I think yes)

In principle it could easily be either way, but the way they've worded it is quite suggestive.

Perhaps it is not wise to speculate, seeing as the writers have succeeded in being very secretive with the results apparent. Let us remember that a non-detection is just as valuable as a detection here.

Pale Red Dot
‏@Pale_red_dot  
Our paper has got positive referee reports! what does this means? Learn about peer review https://palereddot.org/peer-review-or-how-an-experiment-becomes-scientific-literature/ …

Looks like someone may have found something : Scientists to unveil new Earth-like planet: report
http://phys.org/news/2016-08-scientists-unveil-earth-like-planet.html

Triton wrote:

Looks like someone may have found something : Scientists to unveil new Earth-like planet: report
http://phys.org/news/2016-08-scientists-unveil-earth-like-planet.html

I look forward.

"...Scientists are preparing to unveil a new planet in our galactic neighbourhood which is "believed to be Earth-like" and orbits its star at a distance that could favour life, German weekly Der Spiegel reported Friday..."
"The still nameless planet is believed to be Earth-like and orbits at a distance to Proxima Centauri that could allow it to have liquid water on its surface—an important requirement for the emergence of life," said the magazine

FABULOUS !!!!

http://www.universetoday.com/130276/earth-like-planet-around-proxima-centauri-discovered/

Discovered by the same team that "discovered" Alpha Centauri B b. I am highly skeptical of this new one.

Unless I've missed something, where it stands today, this is a single rumour being spread by someone at Der Spiegel. So not only is this going through a bit of a game of "telephone" where someone who works with ESO talked with an interviewer who probably doesn't understand the nuances of the science, it's also being written up with a sensationalist filter specifically skewed to make the story more click-bait worthy. I really don't see a reason to be excited about this yet.

This could easily be a case where a 1.5 sigma detection of an RV signal (which unbeknownst to us at this point is actually stellar activity) corresponding to a 2 Earth-mass planet in a close-in orbit is being portrayed as a lush, jungle-filled world with kittens rolling around in fields swatting at butterflies. Expectations are roaming wild here.

I am a crazy cat daddy though, so that would be nice to live on such a world.