TESS, Three Stars and a Planet’s Odd Orbit

Transiting Exoplanet Survey Satellite (TESS), a robotic observatory, began watching 200,000 nearby stars on August 7, 2018.

So far, scientists have found more than 2,200 TESS Objects of Interest (TOI). Of these, again so far, 154 have turned out to be exoplanets.

They include a few probably-rocky planets around Earth’s size, but none are ‘Earth 2.0.’ And some are like nothing in our Solar System.

HD 202772A b, for example, is as massive as Jupiter, but orbits its sun every 3.3 days.

Its sun, HD 202772A, is larger and hotter than ours; so the planet is a great deal hotter than Jupiter. Scientists figure its equilibrium temperature is around 2,100 K.

That’s hot enough to melt platinum or thorium, but not quite Thulium’s boiling point. At Earth’s sea-level atmospheric pressure.1

TESS, a Space Observatory

Artist's concept of NASA's TESS space observatory. (2014)
(From NASA, via Wikimedia Commons, used w/o permission.)
(TESS, Transiting Exoplanet Survey Satellite; Artist’s concept.)

Depending on what’s being discussed, Tess is “Tess of the d’Urbervilles,” Hardy’s durable novel; or Nikolay Tess, a fall guy in Latvia. It’s also a British musician; or any one of 13 tropical storms.

I’m guessing that NASA didn’t have “Tess of the d’Urbervilles” in mind when they named their Transiting Exoplanet Survey Satellite.

On the other hand, maybe the moniker’s an effort at appeasing today’s Mrs. Grundys.2 Make that Ms. Grundys, given today’s priggish preferences, and that’s another topic.

Transiting Exoplanets

(From NASA, via Wikimedia Commons, used w/o permission.)
(Almost a full-sky survey: NASA illustration, showing TESS’s overlapping fields of view.)

Back in 2018, when the space observatory went into orbit, TESS was billed as an all-sky transiting exoplanet survey. That’s not quite accurate, although by this time TESS has observed about three-quarters of Earth’s sky.

If you know about transiting exoplanets, TESS and all that, then feel free to skip to the next heading. Or, better yet, take a coffee break, sort your socks or go for a walk.

Still here? Thanks!

Transiting exoplanets aren’t a particular kind of exoplanet, like hot Jupiters, Mini-Neptunes or Super-Earths.

They’re planets orbiting another star with orbits that carry the planet across their sun’s face, as seen from the Solar System.

Astronomers can’t take photos of transiting exoplanets, the way they do when Venus or Mercury passes between our planet and our star, but they can measure how much the star’s light dims during a transit.

And, if the star is bright enough and close enough, measuring how the light changes tells scientists whether the planet has an atmosphere, and what’s in the alien air.

HD 209458 b, for example, the first transiting exoplanet spotted, is also the first known to have an atmosphere. Since 1999, when it was discovered, we’ve learned that there’s hydrogen in its atmosphere. Plus water vapor, carbon dioxide, and methane. Maybe.

HD 209458 b is a hot Jupiter, orbiting a star that’s much like ours, about 159 light-years out in the general direction of Epsilon Pegasi: Enif, the nose of Pegasus.3

Not Quite an All-Sky Survey: Yet

TESS primary mission mosaic. (2014)
(From NASA/MIT/TESS and Ethan Kruse (USRA), used w/o permission.)
(Mosaic showing TESS primary mission survey area. The ecliptic’s on this map’s equator.)

TESS year 1-4 pointings, ecliptic coordinates.
(From MIT/TESS, used w/o permission.)
(TESS year one through four survey areas, ecliptic coordinates.)

Backing up a bit, TESS was billed as an ‘all-sky’ observation mission back in 2018. If the space observatory lasts long enough, it may finally have looked at the entire sky.

But it only covered about 75% of the sky in the two years of its primary mission. That’s because scientists told TESS to look northward of Earth and the Moon, avoiding their scattered light.

And the primary mission’s original planned observations avoided the ecliptic, the plane of Earth’s orbit. I strongly suspect that was because TESS, Earth and our world’s Moon are all in the inner Solar System.

And, since the Solar System’s inner planets, asteroids and zodiacal light’s dust are all in the ecliptic too, observations though all that would have scattered light issues, too.4

KOI-5Ab/TOI-1241b: Yes, It’s a Planet

Caltech/R. Hurt's KOI-5 star system diagram. Not to scale.)
(From Caltech/R. Hurt (IPAC), used w/o permission.)
(The KOI-5 star system. Diagram is not to scale.)

A Tale of Planetary Resurrection
Whitney Clavin, Caltech News (January 11, 2021)

“Shortly after NASA’s Kepler mission began operations back in 2009, it identified what was thought to be a planet about the size of Neptune. Called KOI-5Ab, the planet, which was the second new planet candidate to be found by the mission, was ultimately forgotten as Kepler racked up more and more planet discoveries. By the end of its mission in 2018, Kepler had discovered a whopping 2,394 exoplanets, or planets orbiting stars beyond our sun, and an additional 2,366 exoplanet candidates, including KOI-5Ab.

“Now, David Ciardi, chief scientist of NASA’s Exoplanet Science Institute (NExScI), located at Caltech’s IPAC, says he has ‘resurrected KOI-5Ab from the dead,’ thanks to new observations from NASA’s TESS (Transiting Exoplanet Survey Satellite) mission.

“‘KOI-5Ab fell off the table and was forgotten,’ says Ciardi, who presented the findings at a virtual meeting of the American Astronomical Society (AAS)….”

KOI-5Ab may have been forgotten by humans, but Kepler’s observations remained in our databases. And, happily, someone noticed that TOI-1241b in the TESS databases was the same as KOI-5Ab; so scientists could verify that KOI-5Ab was a planet.

Adriaen van de Venne's illustration of a 'Dutch telescope' in Johan de Brune's 'Emblemata of zinne-werck.' (1624)Verifying that KOI-5Ab/TOI-1241b’s existence had been confirmed took more time than I liked.

Partly because that particular star system’s designation isn’t quite standardized.

On the other hand, we’re well past the days when four astronomers could say Aschere, Al Shira, Lubdhaka and Sirius: and be talking about Alpha Canis Majoris. (September 18, 2021)

But I learned that The Extrasolar Planet Encyclopaedia’s “Planet Kepler-5 b” was at the same coordinates as KOI-5AB and TOI-1241b.5 It’s real.

And it’s not quite like anything in the Solar System.

TOI-1241b’s Oddly Skewed Orbit

Caltech/R. Hurt's KOI-5 star system diagram. Not to scale.)
(From Caltech/R. Hurt (IPAC), used w/o permission.)
(Artist’s impression of KOI-5Ab/TOI-1241b.)

KOI-5Ab/TOI-1241b’s mass is about half that of Saturn’s. It circles its sun every five days, more or less.

KOI-5A is a bit more massive and hotter than our star, so KOI-5Ab/TOI-1241b too massive and far too hot to be ‘Earth-like.’

KOI-5A and B orbit each other every 30 years. KOI-5C goes around A and B every 400 years. That’s roughly 30 and 400 years.

If what we know about how planetary systems grow is right, then KOI-5Ab/TOI-1241b’s orbit should be in the same plane as the two brightest stars’ orbit. But it’s not.

KOI-5Ab/TOI-1241b’s orbit is tilted about 50 degrees out of what should be its ecliptic. Scientists aren’t sure why, but think it’s likely that KOI-B’s gravity messed with KOI-5Ab’s original orbit.

Studying the KOI-5/TOI-1241 and other multiple-star planetary systems should help scientists learn more about how stars and planets form.6

There’s more to say about TESS, exoplanets and stars, much more; but that’ll have to wait for another time.

My right shoulder has been acting up, making writing a slower process than I like.

An ‘up’ side is that it’s giving me opportunities for practicing patience, and that’s yet another topic.

Let’s see. How should I wrap this up? Rattle off statistics? Complain about being 70 — which would be daft, considering the alternative. Got it! Travelogue.

KOI-5Ab/TOI-1241b’s planetary system is 2,950 light-years out, give or take. That’s far outside TESS’s 200 light-year search bubble. So I figure TOI-1241b is a sort of bonus, confirming Kepler observations.

At any rate, KOI-5Ab/TOI-1241b is by far not the first stellar system we’ll visit.

Stellar Stopover Speculation

AllenMcC.'s two-dimensional illustration of an Alcubierre metric tensor. (2007)But if and when we do send probes out there, they’ll pass Delta and Gamma Cygni, Fawaris and Sadir, on their way.

Or maybe they’ll stop off at Fawaris and Sadir, assuming that whatever technology we use allows such stopovers.7 And that’s yet again another topic.

I’ve talked about TESS, exoplanets and all that before, and probably will again:

1 TESS and metals:

2 Monikers, moralists, a musician and more:

3 Stars and planets seen in silhouette:

4 Choosing undusty skies:

5 Kepler-5’s planet: verified!:

6 Catchy Title, Solid Science:

7 Stars and speculation:

About Brian H. Gill

I was born in 1951. I'm a husband, father and grandfather. One of the kids graduated from college in December, 2008, and is helping her husband run businesses and raise my granddaughter; another is a cartoonist and artist; #3 daughter is a writer; my son is developing a digital game with #3 and #1 daughters. I'm also a writer and artist.
This entry was posted in Exoplanets and Aliens, Science News, Series and tagged , , , . Bookmark the permalink.

2 Responses to TESS, Three Stars and a Planet’s Odd Orbit

  1. Your articles are so well researched, Brian. Thank you so much. Amazing.

    God bless.

Thanks for taking time to comment!