Exoplanet detection news

[Cancer]

Several big surveys for detection of extrasolar planets by means of photometry rather than spectroscopy are starting to pay off.

Spectroscopy detects planets via the Doppler effect, measuring the reflex velocity of the star caused by the gravity of a planet going around it. Approximately all the extrasolar planets found in the last dozen years have come by this technique. Advantage: you don't have to stare at the star, just observe it every so often; and you can see a bigger fraction of the planets that are out there. Disadvantage: you can only observe one star at a time, and it takes a lot of light to get spectra of the requisite accuracy, which means it takes large telescopes (about 3 meters and up).

Photometry is measuring the apparent brightness of an object. To detect planets this way, you stare at a piece of sky and see if any of the stars there get periodically fainter by about 1%, when the planet goes in front of the star and blocks some of the light. Advantage: requires much smaller telescopes (~1 meter is adequate), and you can measure all the stars in a field at once; an also be done efficiently which much fainter stars than the spectroscopic technique. Disadvantage: you only detect those which transit, i.e., the orbit is exactly edge-on to us, which is a much smaller fraction of the planets that are out there.

Important point: Only using both techniques can you measure the radius of the planet. With an orbit you get a mass for the planet, and combining mass & radius you get a density, which is a very crude tool toward estimating the overall composition of the planet. (Jupiters have densities like 1 ton per cubic meter; rocky planets are 3 tons per cubic meter and up.)

Both techniques strongly favor detection of "hot Jupiters", that is, big massive planets very close to the central stars. Seems that some of those are bigger and fluffier than predicted. Standard models include the effects being warmed by the star, which causes the outer envelope of the planet to expand under the heat, but something else must be going on in some cases. From the April 1 2007 issue of Astrophysical Journal:


Only a month ago, HD 209458b was the single known case of a hot Jupiter that is almost certainly too large to be explained by standard models of planetary structure.... With only one strong anomaly [i.e., when only HD209458b was known], explanations requiring somewhat improbable events were perfectly viable. However, now that a significant fraction [4 of 9, including Jupiter and Saturn would boost the 9 to 11] of the transiting hot Jupiters are found to be similarly in need of this additional energy, the burden of the theorists may shift to seeking explanations for this effect that are more generally applicable.

These hot Jupiters have radii about 10 to 15 % of the radii of the central stars; the ones that are too big are larger than model predictions by as much as 50% or so. FWIW, these planets that are "too large" are all in orbit around K stars rather than F or G stars; it isn't clear yet whether that's important, or what it might mean if it was important.

[Old Man]

That could be anything. It could be that K stars emit too weakly and so the oversized planets are able to hoover up more volatiles during accretion. Or tidal forces could be to blame. Or it could be some kind of statistical or spectroscopic error in the measurements that just exaggerates the perceived Doppler effect on K stars.

[Cancer]

I tend to agree with you. I'm pleased that the photometry guys are staring to have discoveries fall out of the pipeline. Those have somewhat different systematic detection effects than the spectroscopists, so we can expect results that disagree over the next few years. And disagreement is where you start learning good stuff.

[Basil]

That could be anything. It could be that K stars emit too weakly and so the oversized planets are able to hoover up more volatiles during accretion. Or tidal forces could be to blame. Or it could be some kind of statistical or spectroscopic error in the measurements that just exaggerates the perceived Doppler effect on K stars.

I'm afraid you misunderstood in what sense the hot Jupiters are "too big." It's not a matter of their masses, but of their radii. Given mass and temperature, the expected radius can be deduced. However, among such hot Jupiters as have had their radii "measured," almost half have radii larger than what the best current models predict.

Thus, either the measurements are wrong, or the models are. But if the measurements are wrong, they are so in the same "direction" nearly half the time, which suggests something fairly fundemental is flawed in how the measurements are taken. In either case, interesting times are ahead. :)

[Old Man]

I'm afraid you misunderstood in what sense the hot Jupiters are "too big." It's not a matter of their masses, but of their radii. Given mass and temperature, the expected radius can be deduced. However, among such hot Jupiters as have had their radii "measured," almost half have radii larger than what the best current models predict.

That's exactly what I meant. Accretion of more, lighter volatiles should create larger planets (as measured by radii) for given mass. Not sure if that would enlarge them to the point that is being observed, though. There's only one way to find out.

[Cancer]

In the paper this morning was an announcement by the Swiss team that they'd found an Earth-class planet in a star's habitable zone.

The star is Gliese 581, an M2.5V red dwarf. This star was previously known to have a planet, designated Gl 581b, with a 5.36-day orbital period (assuming the star has a mass of 0.31 solar masses, that turns into an orbital size of 0.041 AU); this planet is inferred to be about the mass of Neptune (15.6 times the mass of Earth).

Two new ones were announced this morning. "c" has a mass of 1.6 Earth, an orbital period of 12.91 days, and again assuming the stellar mass that's an orbital size of 0.073 AU. "d" is about 8 Earth masses, period 84.4 days, 0.25 AU.

Taking the luminosity of an M3V star and those orbital parameters for "c", then the surface temperature of the planet (assuming it has a surface) is within howling distance of the temperature range for the existance of water in its liquid form. There's lots of "if's" in that conclusion.

The technical preprint is at this site (http://obswww.unige.ch/~udry/udry_preprint.pdf). They present solutions for both circular (that is, eccentricity fixed at 0.0)orbits and fit eccentricities; for the last planet in particular the fit eccentricity (0.2 +/- .1) is of marginal significance. The span of observations in the solution is only 1050 days; I'd like to see that doubled or tripled and a better solution obtained. But considering the nature of the planet-finding racket, I'm not surprised they went public with it now.

[Jaxom]

Interesting... With those numbers I would expect tidal locking for b and maybe c. The numbers don't look like any ratios I would expect though. C and d show a possible ratio of 6 or 7 to 1 which is also not one I recall being stable for resonance.

[Cancer]

Yeah, the strength of the orbital solution for d isn't great. It's the circumstances of c that led to the pressure to take it public. IMO they really need 2-3 times as many data points as they have for good solutions for d, and to firm up c more.

[Basil]

Boy, and here I thought I'd surprise everyone with this (http://seattletimes.nwsource.com/html/nationworld/2003680170_planet25.html)article. Seems Cancer's got much better info.

Thanks, Cancer! ;)

[Outsider]

OK, so spectroscopy detects planets by seeing the wobble they cause in the star. More massive planets = more wobble = easier to detect.

Photometry = detecting planets by seeing the star dim as they pass between us and it. Bigger planets = more light blocked = easier to detect.

In both cases planets closer to their parent star will be eaiser to detect as both wobble (gravity effect) and light blockage (size effect) willl be more pronounced if the planet is closer.

Combining the two one can measure both mass and volume, and thus get density.

It doesnt seem to me that the density thus derived would be very accurate, though, being that errors in the two measurements used to calculation it would be compounded. Maybe enough to say "Gas Giant" or "Rocky Planet" but not enough to say "1.5 times earth sized" vs "2 times earth sized".

How much of that kind of declaration is guesswork, do you think? basically, how accurate are spectroscopy & photometry in this application?


(note : the difference between 1.5 and 2.0 diameters in a 5 earth mass planet means a difference in surface gravity of 2.2Gs vs 1.2Gs...)

[Cancer]

There is no concrete information about the radius of planet c. They don't have photometry; it's purely a spectroscopic result. The stuff in the press about planet radius and size come from the planet mass (which is a lower limit obtained in the spectroscopic orbit solution) and then assuming a density.

In our Solar System, the terrestrial planets' densities range from about 3.5 to about 5.5 (the units are g/cm^3 = T/m^3); the Jovian planets are 2ish down to 0.7, IIRC.

Known exoplanet densities are limited to hot Jupiters so far, and are even lower still. Presumably that's due to heating "fluffing up" the gaseous outer layers of the jovian planets, though there are problems with that situation.

Back to this particular case ... M2.5V stars commonly have spots. I think Gliese 581 is among those known to, in fact. If you have spots on the photosphere, that greatly complicates any attempt to find a planet by eclipses.

[L. Marcus]

. . . Damn spots!

[Nyrath]

There is some analysis on the finding here:
http://oklo.org/?p=206
http://oklo.org/?p=207

[L. Marcus]

. . . So those guys expect a water world? And a transition on the 7th?!

[Cancer]

New item in the Astrophysical Journal (http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v661n1/21184/brief/21184.abstract.html) yesterday, a (big Jupiter class) planet found orbiting epsilon Tauri.

Nothing special about the planet itself: minimum mass of 7.6 Jupiters, 595 day orbital period, orbit size of 1.93 AU.

What's special is the host star. It's one of the Hyades giants; the Hyades are a nearby open star cluster about 45 parsecs away (they make up most of the "V" that is the "face" of Taurus) that has been intensely studied for over fifty years. Epsilon Tau is one of four red giants in that cluster, and as such, we know just about all there is to know about it.

The cluster is 625 million years old ... relatively young. It's metal rich (this is pretty common for young stars and for stars with planets). And the cluster has been surveyed pretty hard for planets, and none have been found around the dwarfs (main sequence stars) in the cluster. There could be good reasons for that (young stars have more chromospheric activity which makes detecting the velocity variations caused by a planet more difficult to detect), but it's still a little odd to find a planet orbiting a giant.

The other that we know is that the star has a mass of about 2.7 solar masses, which is more massive than any of the planetary host stars previously detected. It was (when on the main sequence) an A0 or A1 star, like Vega or Sirius; details of the spectral lines in such stars make it more or less impossible to detect planet-induced velocity changes in such stars; it's not a technology problem, it's intrinsic in the spectra of early A-type stars. So the reason none have been found orbiting such stars before is because it wouldn't be possible to detect them if they were present.

So, clear proof that more massive stars can have planets. No one is surprised, but it wasn't proven before.

Though arguing from a sample size of 1 is hazardous :rolleyes: the detection of a planet orbiting a giant rather than in any of the 100 or so lower-mass main sequence stars in the cluster is a weak suggestion that perhaps more massive stars are more likely to have planets than less massive ones. That's an interesting suggestion ... given that massive stars don't last long, that would suggest there's lots and lots of planets out there orbiting dead white dwarfs or floatign in free space after the massive star died off and lost a lot of mass ... mass loss lowers the gravitational binding energy and can make orbits become unbound.

FWIW, the 1.93 AU orbit size is larger than many orbits, but given the star has been through the tip of the red giant branch and is now back on the core helium burning red giant clump, its radius has been as large as about 1AU in the past, and it would have consumed any and all planets that had been within 1 AU of the star, so those in larger orbits are all that would have survived to be detected now.

[EDIT: misremembered the stellar mass; it's 2.7 solar masses, not 2.]

[L. Marcus]

*sits up in bench, pays attention, takes notes and records lecture*

[Cancer]

This might be in the morning newspapers: they've found another couple of planets in the Gliese 581 system, one of them (GJ 581 g) with a mass 3.1 Earth masses, with an approximately circular 36.5-day orbit around an M3V star that is plausibly in the in the habitable zone. I'll be reading the preprint overnight.

[dmjalund]

you know, "Hot Jupiter" sounds like an exclamation made by a Side Kick in a 1950's Pulp SF comic

[McCoy]

In the paper this morning was an announcement by the Swiss team that they'd found an Earth-class planet in a star's habitable zone.
"Earth-class" in this context means Earth mass (more or less)?

[Old Man]

3.1 Earth masses and at the appropriate distance from its star to have liquid water. Whether it actually has any water would require further observation.

Gliese 581 is only 20 ly away. Road trip anyone?

[Lucius]

3.1 Earth masses and at the appropriate distance from its star to have liquid water. Whether it actually has any water would require further observation.

Gliese 581 is only 20 ly away. Road trip anyone?

Count me in!

Wasn't Susano supposed to be finding us some ships and proper sails? He will find there are men here, too, who do not fear the appalling distance.

Lucius Alexander

The palindromedary crunches some numbers

[megaplayboy]

at 1 percent of lightspeed, a mere 2000 years away.

[IndianaJoe3]

at 1 percent of lightspeed, a mere 2000 years away.

An Orion might be able to get up to 10% of c, so it's only 200 years away.

[austenandrews]

An Orion might be able to get up to 10% of c, so it's only 200 years away.
In a century or two, that should be within the average lifespan. Sweet! :p

[Cancer]

The GJ 581 primary is M3V, so it'll be rather deficient in ultraviolet. Tanning beds required.

The thing with an orbit that close to the star is that the planet almost certainly is tidally locked, so that there's a "day side" and a "night side".

[Old Man]

In a century or two, that should be within the average lifespan. Sweet! :p

The exact travel time isn't as important in my case since I'm immortal.

Apparently the planet has already been named "Gloaming", though by whom, I don't know. AFAIC if I get there first I get to call it whatever I want.

[austenandrews]

Gloaming is cool too.

[Cancer]

It's better than, say, "Barstow" or "Newark" or "Joliet" or "Fort Stockton".

[Lucius]

An Orion might be able to get up to 10% of c, so it's only 200 years away.

Given time dilation effects, how long is that for the people actually making the trip?

Lucius Alexander

Measures all things relative to the palindromedary

[Captain Obvious]

Given time dilation effects, how long is that for the people actually making the trip?

Lucius Alexander

Measures all things relative to the palindromedary

Still over 190 years, if I'm not mistaken. Which, I guess, means you can spend a few years at the rest stop and it won't really matter.

[McCoy]

Given time dilation effects, how long is that for the people actually making the trip?

Lucius Alexander

Measures all things relative to the palindromedary
IIRC, it's been a while since I've done the math, time dilation isn't that significant until you get above .7 c.

[dmjalund]

but I'm sure we could achieve a suspended animation between now and then

[Old Man]

It's better than, say, "Barstow" or "Newark" or "Joliet" or "Fort Stockton".

"New Barstow" FTW!

[Markdoc]

I'm rather fond of "Great Cockup" from England's Lake District :)

Or the ever-popular but NSFW Fucking, Austria (http://www.snopes.com/photos/signs/austria.asp)

cheers, Mark

[Old Man]

Well, now that we've found another possibly habitable world, I think we should waste no time in screwing it up. What's stopping a billionaire from sending their own space probe full of robotic oil drilling rigs and genetically modified kudzu?

[Captain Obvious]

Who's to say kudzu will even survive there? It might be daisies or tomatoes or clover that goes nuts growing in those conditions and won't be eaten by the native life.

[Old Man]

Bermuda grass then. That stuff grows like crazy anywhere it's not supposed to.

[Old Man]

But wait! Now it's named Zarmina! (http://io9.com/5653433/the-astrophysicist-who-discovered-zarmina-describes-life-on-second-earth)

[Xavier Onassiss]

Who's to say kudzu will even survive there? It might be daisies or tomatoes or clover that goes nuts growing in those conditions and won't be eaten by the native life.

Cap, this is KUDZU we're talking about here: the plant kingdom's answer to cockroaches. It grows so fast it might get to gleise 581 before we do.

Never doubt the power of kudzu. http://www.herogames.com/forums/attachment.php?attachmentid=35761&d=1272506218

[Lucius]

But wait! Now it's named Zarmina! (http://io9.com/5653433/the-astrophysicist-who-discovered-zarmina-describes-life-on-second-earth)

"Maybe you won't be filming Corona commercials on the beach there but it will be life."

Lucius Alexander

But can a palindromedary survive there?

[Lucius]

Cap, this is KUDZU we're talking about here: the plant kingdom's answer to cockroaches. It grows so fast it might get to gleise 581 before we do.

Never doubt the power of kudzu. http://www.herogames.com/forums/attachment.php?attachmentid=35761&d=1272506218

I hope not.

It's called "Foot a day vine" and I have read that sometimes it can double even that.

That's a very impressive plant, but even so, I figure it would take billions of years to reach the Gliese system at that rate.

Lucius Alexander

The palindromedary recommends adding Megascale to the plant's Growth

[Querysphinx]

Sitting here wondering just how frigging hard it would be to hit that planet with say a probe even if we could get a meaningful probe up to .1 c.

[Tasha]

I also thought that it was interesting that he was looking at a gaggle of the nearest Red Dwarf stars for earthlike exoplanets. Perhaps he will find one that's even better than Zarmina.

It's kind like the Guy that runs the Oz SETI project who is looking in the same neighborhood for stars emiting light in the laser spectrum, that might contain some sort of signal. We live in very interesting times.

[Xavier Onassiss]

I hope not.

It's called "Foot a day vine" and I have read that sometimes it can double even that.

That's a very impressive plant, but even so, I figure it would take billions of years to reach the Gliese system at that rate.

Lucius Alexander

The palindromedary recommends adding Megascale to the plant's Growth

That's two feet a day in normal gravity. But if that stuff figures out how to reach orbit, watch out.

I'm just sayin'.

[L. Marcus]

... Super Mario Bros. ^^

[The Weapon]

I'm rather fond of "Great Cockup" from England's Lake District :)

Or the ever-popular but NSFW Fucking, Austria (http://www.snopes.com/photos/signs/austria.asp)

cheers, Mark


That's what the Germans said when they gave them that megalomaniac that thought he was a painter.

[The Weapon]

IIRC, it's been a while since I've done the math, time dilation isn't that significant until you get above .7 c.

At 10% it's Sqrt(1-(10%)^2) ~= .95.

I tried to upload a spreadsheet but I'm having problems. So here's a few values.
Fraction of c Time dilation Mass inc.
0.01___ 0.999949999___1.00005
0.02___0.99979998___1.0002
0.03___0.999549899 ___ 1.00045
0.04___0.9919968___ 1.000801
0.05___0.998749218___1.001252
0.06___0.998198377___1.001805
0.07___ 0.997546991___1.002459
0.08___ 0.996794864___1.003215
0.09___0.995941765___1.004075
0.1___0.994987437___ 1.005038
0.15___ 0.988685997___1.011443
0.2 ___0.979795897___ 1.020621
0.25___ 0.968245837___1.032796
0.3___ 0.953939201___ 1.048285
0.35___0.9367497___1.067521
0.4___ 0.916515139___1.091089
0.45___0.893028555___1.119785
0.5___ 0.866025404___ 1.154701
0.55___ 0.835164654___1.197369
0.6___ 0.8___________ 1.25
0.65___ 0.759934208 ___ 1.315903
0.7___0.714142843_____1.40028
0.75___ 0.661437828____1.511858
0.8___ 0.6____________1.666667
0.85__ 0.526782688______1.898316
0.9__ 0.435889894______ 2.294157
0.95__0.3122499________ 3.202563
0.96__0.28____________3.571429
0.97__ 0.243104916______4.11345
0.98__0.198997487 ______5.025189
0.99__ 0.14106736______7.088812

[L. Marcus]

That'd be sqrt (1 - (0.1^2/1^2)) = sqrt (1 - 0.01) = sqrt (0.99), which is as close to 1 as makes not much practical difference.

0.7 c would give sqrt (1 - (0.7^2/1^2)) = sqrt (1 - 0.49) = sqrt 0.51, which rounds off as 0.71.

If we say that a time dilation of 0.95 would be the limit of humans noticing it, that'd give a speed of about 0.31c.

[Cancer]

Sitting here wondering just how frigging hard it would be to hit that planet with say a probe even if we could get a meaningful probe up to .1 c.

Well, the system is 6.7 parsecs away. That means that the 0.3 AU orbit of the planet subtends 0.045 arc seconds as seen from here. You can't really reach that aiming precision from earth's surface, but from space it's easy. Hubble Space Telescope can do that routinely, and frankly, that's tech from circa 1980.

So you can aim at the planet orbit from here pretty easily. Aiming at a particular location within that orbit is something else, but you have see where the moons and asteroids belts are from closer in before you can make a safe rendezvous.

[Cancer]

"Maybe you won't be filming Corona commercials on the beach there but it will be life."

Lucius Alexander

But can a palindromedary survive there?

Is that ads for Corona Borealis (http://en.wikipedia.org/wiki/Corona_Borealis) or Corona Australis (http://en.wikipedia.org/wiki/Corona_Australis)?

:rolleyes:

[Cancer]

... Aaaaand in this morning's paper is a mention of the Kepler-11 system (http://www.nasa.gov/mission_pages/kepler/news/new_planetary_system.html), which was published yesterday in Nature.

A more-or-less Sun-like star ("Teff = 5,680 ± 100 K, surface gravity g of log[g (cm s−2)] = 4.3 ± 0.2, metallicity of [Fe/H] = 0.0 ± 0.1 dex, and an projected stellar equatorial rotation of vsini = 0.4 ± 0.5 km s−1. Combining these measurements with stellar evolutionary tracks ... yields estimates of the star’s mass, 0.95 ± 0.10 M⊙, and radius, 1.1 ± 0.1 R⊙, where the subscript ⊙ signifies solar values.") with six planets now known to be orbiting it.

(For reference, the Sun has Teff = 5780 K, log g = 4.44 in the same system of units, [Fe/H] = 0 by definition, and an equatorial rotation speed of a hair less than 2.0 km/s.)

The planets' masses range from 2.3 to 13.5 times Earth (the outermost planet doesn't have a mass estimate yet); the two innermost ones have densities of 3.1 and 2.3 grams per cc (= metric tons per cubic meter). The others are less than 1. For comparison, Uranus is 14.5 Earth masses; but in our Solar System, only the larger moons of the giant planets have densities in that range, and those have large amounts of ice. These guys can't have ice. Before these planets might have been labeled "super-Earths" but the low densities make them rather different from the terrestrial planets we know.

All their orbits are smaller <= 0.462 AU. Only one of them has an orbital size (and period) larger than Mercury's. So they are all pretty close to the star and therefore pretty warm, probably Venus-like surface temperatures in the simplest possible models (there is no direct information about this in the available data).

Interesting was another comment in the paper that the Kepler mission has 1200+ candidate planets now. That seems to have been just a press conference, without the hard data I want to find.

[austenandrews]

Before these planets might have been labeled "super-Earths" but the low densities make them rather different from the terrestrial planets we know.
Are there any prominent theories as to what these things might look like up close?

[Cancer]

Not that I've heard. Figure 5 from that Nature paper puts these planets on a graph of radius versus mass with curves for various compositions. Planet b is spang on a curve for something that is 50% water by mass (the rest is a metal/rock core and atmosphere) but the temperature (about 900 K) is much too high to be anything familiar. Probably something gas-giant-ish is the best guess, but we have no good analogs of these guys in our Solar System.

[megaplayboy]

We probably need to get to about 10,000 detected Earth-size planets in the habitable zones of stars, before a real significant chance of discovering ET life is sufficient to justify fast unmanned sublight probes/explorers sent to everything within 100-200 LY of us. Even then, it may take millenia for us to colonize something outside our own solar system. I guess we could find an uninhabitable planet and cannibalize resources to build a large orbital colony there, though.

[Cancer]

Their press conference said 1235 candidate planets and 54 Habitable Zone candidates. Unfortunately, that's the only numbers available, and those are almost devoid of context. There is the key quoted comment, "Five of the planetary candidates are both near Earth-size and orbit in the habitable zone of their parent stars."

[McCoy]

Their press conference said 1235 candidate planets and 54 Habitable Zone candidates. Unfortunately, that's the only numbers available, and those are almost devoid of context. There is the key quoted comment, "Five of the planetary candidates are both near Earth-size and orbit in the habitable zone of their parent stars."
To clairify, "near Earth-size" in this context is 10 Earth-masses or less?

[Escafarc]

To clairify, "near Earth-size" in this context is 10 Earth-masses or less?

Well I guess obesity is a growing problem everywhere.

[Cancer]

To clairify, "near Earth-size" in this context is 10 Earth-masses or less?

I don't know. Literally the only information here is the sentence I quoted.

If I had to guess, "near Earth-size" here refers to planetary diameter. Kepler is an instrument that looks for eclipses made by planets blundering in front of stars, so the thing that comes out of its raw data is an estimate of the duration and depth of eclipses, both of which depend on planetary diameter. But that is a guess on my part. I've been rooting around for other more detailed information and come up empty so far.

[megaplayboy]

Anyone know how many exo-planets have been detected within, say, 20 to 200 light years?

I think that would be the practical range, where an advanced probe moving at 1 to 10% of lightspeed could be sent to probe/explore them.

[Cancer]

My guess is that just about anything with a Greek letter designation or an HD or HIP or GJ number will most likely be within 100 parsecs (326 light-years). There are some on-line tools for playing with published exoplanet data, most notably http://exoplanets.org/table/ . Just applying a parallax filter, only 82 of 427 have parallaxes smaller than 10 milliarcseconds (which is a fancy way of saying: further than 100 parsecs). Most of the early searches focussed on bright stars, which necessarily are nearby ones.

[Cancer]

I missed this when it came out a couple of months ago, but HIP 13044 was found to have a planet as well. This made for some hoopla.

HIP 13044 is a metal-poor star, which probably, but not quite certainly, means it is quite old: probably around 10 Gyr or perhaps a bit more. The metallicity value (-2.09, which means its iron content is about 1/120 that of the Sun) isn't quite bulletproof from my point of view but it's almost certainly in the right ball park. If that metallicity is right, it is the lowest known metallicity for a planet-hosting star.

The star is vehemently suspected of originating in a galaxy that has since been destroyed and incorporated into our own, so it got announced as "a planet of extragalactic origin". There's clearly lots of those stars that have been annexed into our Galaxy, so IMO the only thing unusual about this is that the evidence for said origin is clear.

The star is also a "horizontal branch" star, which means it is between red giant stages. It has been a red giant star before, and will be again. That means any close-in planets that were in the system have been consumed already. There are a few other red giant stars known to have planets, though.

The combination of metal-poor, old, and post-main-sequence is extreme in all senses, and more or less takes any hard limits away from where one might think one could find a planet. The only exception to that is ... you won't find a planet in space that used to be inside the star. For stars that used to be red giants, any planets that were within ~1 AU of the star got consumed during the red giant phase.