A Doomed World, Spiraling to Destruction

NASA's illustration: Kepler-1658 b, a previously-discovered hot Jupiter which recent data and analysis says may be spiraling into its host star. (December 19, 2022)
Artist’s impression: Kepler-1658 b, a “hot Jupiter” in a decaying orbit. (December 19, 2022)

Kepler-1658 b, KOI-4.01, is a “hot Jupiter”. In another 2,500,000 years, give or take a bit, it won’t be there any more.

That makes it a hot subject for scientists: literally and figuratively.

Kepler-1658 b is also the the Kepler space telescope’s first confirmed exoplanet.

Frederik de Wit's 'Planisphaerium coeleste' star chart. (1670) Frederik de Wit, via Wikimedia Commons, used w/o permission.As usual, the star KOI-4 (the fourth star observed by the Kepler space telescope) had a whole mess of other designations: 2MASS J19372557+3856505, KIC 3861595, TYC 3135-652-1 and WISE J193725.57+385650.4.

But never mind that. I’ve talked about star names and designations before:

Besides, today I’ll be talking about Kepler-1658 b and why studying it matters.

To scientists, at any rate.

Kepler-1658 b, Designations and “Dunkelheim”, a Dark World

Jim Cornmell's sky chart of Caldwell Objects (September 3, 2006)) via Wikipedia, used w/o permission.Kepler-1658 b, KOI-4.01, was the first exoplanet discovered by the Kepler space telescope team.

Then how come it’s not Kepler-1 b, or KOI-1.01?

And, more to the point, why are scientists so interested in this distant world?

Kepler-1658 b’s designations are easier to explain, so I’ll start with that.

KOI stands for Kepler Object of Interest. It’s a list of 150,000 stars observed by the Kepler space telescope.

The KOI list is a subset of the KIC, Kepler Input Catalog’s 13,200,000 stars, give or take.

With nearly two dozen major current star catalogs, why make another one?

For one thing, no existing catalog — from the AC to ZC catalogues — had the breadth and depth of information needed for the Kepler space telescope. And that’s another topic.

We knew about KOI-1.01, KOI-2.01 and KOI-3.01 before Kepler began observing.

KOI-1.01, AKA TrES-2b, TrES-2, and Kepler-1b, for example: the darkest known exoplanet. It’s another hot Jupiter, discovered and confirmed in 2006. TrES-2b.

KOI-101 et cetera hasn’t been given an official name to go with its alphabet soup designations, so I’ll dub in Dunkelheim: dark home. Not that I think it’s anyone’s home.

Dunkelheim is yet another hot Jupiter; a little wider and more massive than the Solar System’s Jupiter, and hot: 1,885 Kelvin, give or take. That’s around 1,611 Celsius. It’s also the darkest known planet, darker than coal, reflecting less than 1% of its sun’s light.1

Why Kepler-1658 b isn’t Kepler-1 b

Kepler space telescope's viewing area. Each rectangle rectangles shows where one of Kepler's 95-megapixel charge-coupled device, or CCD cameras is pointed. Scientists selected these areas to avoid the region's brightest stars (the largest black dots).KOI-4 was the first star in the KOI list that hadn’t been previously confirmed as having an exoplanet. So when the Kepler team published a list of possible exoplanets, that made it the first exoplanet candidate discovered by Kepler.

When scientists find evidence that there’s a planet orbiting another star, that’s an exoplanet candidate. If more analysis shows that there exoplanet candidate really is a planet, it’s a confirmed exoplanet. If not, it stays a candidate exoplanet.

KOI-4.01 was an exoplanet candidate in 2009 because Kepler had detected a slight periodic dimming of the star.

Then scientists noticed a second dimming of KOI-4. The second dimming happened when the candidate exoplanet would have gone behind the star relative to Earth.

Since the Kepler team figured KOI-4 was about 1.1 times as wide as our sun, the dips in the star’s brightness would make KOI-4.01 about as wide as Neptune. Which wouldn’t be big enough to account for secondary dip.

And so KOI-4.01 got reclassified as a false alarm.

Provisionally. Conditionally. Until more analysis and data said otherwise. The Kepler-1658 b story is, putting it mildly, complicated.

“…The initial classification in the Kepler Input Catalog (KIC, Brown et al. 2011) for KOI 4 implied a 1.1 solar radius (R ) main-sequence star with an effective temperature (Teff ) of 6240 K (Brown et al. 2011). Based on a primary transit depth of 0.13%, this stellar classification implied that KOI 4 is orbited by a Neptune-sized planet. However, because a deep secondary eclipse was observed, KOI 4.01 was marked as a false positive (FP) in early Kepler KOI catalogs, since a secondary eclipse would not be observable for a Neptune-sized planet orbiting a main sequence star.
“The NASA Exoplanet Archive reveals a more detailed picture of the complex vetting history of Kepler’s first exoplanet candidate. KOI 4.01 was not listed in the first KOI catalog (Borucki et al. 2011a) but appeared as a ‘moderate probability candidate’ in the second KOI catalog (Borucki et al. 2011b), with the host star noted as a rapid rotator (v sin i = 40 km s−1). In the third catalog, Batalha et al. (2013) listed KOI 4.01 as a PC but it was marked back to a FP in the fourth catalog (Burke et al. 2014), likely due to the secondary eclipse….”
(“The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet“, Ashley Chontos et al., The Astronomical Journal (Submitted March 4, 2019))

At any rate, by 2019 scientists had realized that KOI-4 was 2.89 times as wide as our sun. Give or take 0.12.

Ashley Chontos and others took another look at the data, showed that KOI-4.01 is bit wider than Jupiter, and published more than a dozen pages of text, charts, tables and equations explaining why Kepler 1658 b is worth even more study.2

Planetary Systems: the Solar System and Many More

Natalie Batalha's and Wendy Stenzel's chart of exoplanet populations found with Kepler data. (2017) (NASA and Ames Research Center)
Exoplanets, charted by radius and orbital period. From Kepler data.(2017)

When we started looking for planets circling other stars, we figured we’d find planetary systems like our own: small, rocky planets close to the star; gas giants farther out.

If we found any at all. The nebular hypothesis said that most stars should have planets. But it wasn’t the only explanation for how the Solar System began.

Some said that the Solar System began when another star either passed very close to, or hit, ours.

Distances between stars being what they are, that made the formation of a planetary system wildly improbable.

Immanuel Kant, Pierre Laplace or someone else developed the first nebular hypotheses for how our sun got planets. Basically, the idea is that stars and planets start out as clouds of gas and dust. A cloud’s gravity pulls it into an increasingly dense mass.

The collapsing cloud starts spinning — make that spinning faster. Its the angular momentum thing, like a figure skater spinning faster by pulling in his or her arms.

The faster-spinning cloud keeps collapsing. Eventually it’s a disk of gas and dust with a new star in the middle. Then physics happens in the disk, forming planets.3

By 1990, scientists had several reasonable explanations for why the disk would settle into rocky planets near the star and gas giants farther away.

Then we started finding other planetary systems.

Assorted “Firsts”: and Bellerophon, an Exoplanet That Shouldn’t Exist

Artist's impression of extrasolar planets in the pulsar, PSR B1257+12. (2006) From NASA/JPL-Caltech/R. Hurt (SSC), via Wikimedia Commons, used w/o permission.The first confirmed exoplanets, PSR B1257+12 B and PSR B1257+12 C, were close to their star: but their star was a pulsar, which raised a whole mess of questions.

The other first exoplanet discovered, Gamma Cephei Ab — we do have an official name for this one, Tadmor — is more over nine times as massive as Jupiter.

Tadmor’s year is a tad more than 900 days long. Which is not why it’s called Tadmor.

Tadmor’s discovery was in 1988, when some Canadian scientists said they’d found evidence that Gamma Cephei A had a planet. Then in 2002, other scientists confirmed that Gamma Cephei Ab was a planet, not something else

PSR B1257+12 B and PSR B1257+12 C, were the first confirmed exoplanets.

They were also the first known super-Earths. Super-Earths are (almost certainly rocky) planets more massive than Earth but less massive than Saturn, Uranus or Neptune.

There’s nothing like super-Earths in the Solar System, and we had more surprises coming.

The first planet found orbiting a main-sequence star was 51 Pegasi b, confirmed in 1995.

The planet’s official name is Dimidium, some folks call it Bellerophon, and I am not diving down that rabbit hole.

Dimidium/Bellerophon’s star, 51 Pegasi, is a little more massive, wider, and brighter than ours: but not by much.

Bellerophon, on the other hand, isn’t like anything in our Solar System.

It’s roughly half Jupiter’s mass — that’s not the odd part — but it whips around its star about every four and a quarter days. That’s because it’s only 0.0527 astronomical units away from 51 Pegasi.

By comparison, Mercury’s orbiting our star at about 0.387 astronomical units.

If then-current explanations of how planets form were right, Bellerophon shouldn’t have been there. But it was.

Then we started finding a whole lot more hot Jupiters.4

Finding Strange New Worlds

NASA/JPL-Caltech's illustration: TRAPPIST-1 and Solar planetary systems (February 22, 2017)
Illustration: TRAPPIST-1 and Solar planetary systems, TRAPPIST-1 system enlarged 25x. (2017)

Hot Jupiters, gas giants orbiting close to their stars, aren’t uncommon. But they’re not as common as it looked a couple decades back.

Early methods for detecting planets were good at spotting massive planets orbiting very close to their stars. Small wonder we found so many, early on.

Also small wonder we haven’t found a planetary system that’s pretty much like ours. Not yet, at any rate. New methods and data accumulating since the early 1990s has been letting scientists detect less massive planets in larger orbits.

But we’d still be hard-pressed to detect a planetary system like ours, apart maybe around our closest neighbors.

That said, we have found a vaguely-familiar-looking planetary system.

And we’ve been learning a very great deal about planets and planetary systems.5

55 Cancri A’s Planetary System: (Not) Just Like Ours

NASA/JPL-Caltech's artist's concept: two planetary systems - 55 Cancri's (top) and the Solar System. Blue lines show the orbits of planets, including the dwarf planet Pluto in our Solar System. The 55 Cancri system is currently the closest known analogue to our solar system, but it's not all that close. image credit: NASA/JPL-Caltech (2007)
Two planetary systems: 55 Cancri’s and the Solar System. NASA/JPL-Caltech. (2007)

55 Cancri is a binary star. One star, 55 Cancri A, is a K-type star on the main-sequence (probably), smaller and cooler than ours. 55 Cancri B is a red dwarf.

55 Cancri A’s five known planets are in roughly-circular orbits. The most distant one, Lipperhey, is a gas giant and about as far from 55 Cancri A as Jupiter is from our sun.

So far, the 55 Cancri A planetary system sounds a lot like the Solar System.

I figure that’s why 55 Cancri A’s planets — b, c, d, e and f — have names: Galileo, Brahe, Lipperhey, Janssen and Harriot.

But the rest, from Janssen, the nearest its star, to Harriot, in 55 Cancri A’s habitable zone, aren’t quite like anything in our Solar System.

Here’s a quick list and description, in increasing distance from 55 Cancri A:

  • e (Janssen) first super-Earth discovered around a main-sequence star
  • b (Galileo) a hot Jupiter
  • c (Brahe) probably a gas giant, mass similar to Saturn, about 0.24 AU from its star
  • f (Harriot) probably a gas giant, orbiting in 55 Cancri A’s habitable zone
  • d (Lipperhey) a gas giant, orbiting 55 Cancri A at 5.77 AU

Then there’s TOI-2180 b, a gas giant that’s a little closer to its star than Earth is to ours. Depending on which catalog you’re looking at, it orbits TOI-2180 or HD 238894.

Both designations are for the same star. It’s slightly more massive, a little hotter and a whole lot older that our sun.6

And that brings me to why Kepler-1658 b rates so much attention. Almost. First, I’ll talk about why Kepler-1658 b’s star was on the main sequence, and isn’t now.

Life Cycles of Stars

cmglee, NASA Goddard Space Flight Center's illustration: 'Stellar evolution of low-mass (left cycle) and high-mass (right cycle) stars, with examples in italics.' (2014) via Wikimedia Commons, used w/o permission.
Stellar evolution of low-mass and high-mass stars. (2014)

NASA's 'Stellar Evolution' infographic. (Posted July 9, 2012, image created October 13, 2009)Backing up a little, stars begin as collapsing clouds of gas and dust.

After a while, the lump in the middle of the cloud — a protostar, surrounded by a protoplanetary disk in Geek-speak — gets smaller and denser, it gets hotter. For the same reason a bike pump gets hotter after you’ve filled your tires.

When the protostar gets dense and hot enough, its hydrogen starts fusing into helium and the star lights up. What happens after that depends mainly on how massive the star is.7

Mass and the Main Sequence

Unknown author's (probably Prialnik, Dina; 'An Introduction to the Theory of Stellar Structure and Evolution', Cambridge University Press (2000)) Hertzsprung-Russell diagram, showing the evolutionary tracks of stars with different starting masses. Each track starts where the star has evolved to the main sequence and stops when fusion stops (for massive stars) and at the end of the red-giant branch (for stars 1 Solar mass and less). A yellow track is shown for the Sun, which will become a red giant after its main-sequence phase ends before expanding further along the asymptotic giant branch, which will be the last phase in which the Sun undergoes fusion.At this point, I could start rambling on about proton-proton chains and CNO cycles, blue giants and brown dwarfs; and then meander past the asymptotic giant, red giant and subgiant branches.8 But I won’t.

Although I’d better say a little about the subgiant branch.

How long a star stays on the main sequence depends on how much mass it starts with. Basically, the heavier a star is, the less time it spends on the main sequence.

When stars with between six tenths and ten Solar masses — mid-sized stars — start running out of hydrogen, they get bigger and brighter and move onto the subgiant branch.

Kepler 1658 b’s star — yes! I am finally back to Kepler 1658 b — is about 1.45 times our sun’s mass, and nearly three times as wide. It’s a spectral class F star that’s running out of fuel and has moved onto the subgiant branch.

And that’s why studying 1658 b matters.9 To scientists, anyway. Some scientists, that is, and science fans like me.

Science, Kepler-1658 b and Me

Ashley Chontos et al., 'Figure 3. Surface gravity versus effection temperature for confirmed Kepler exoplanet hosts. Gray points represent confirmed hosts, with known asteroseismic hosts in black. Kepler-1658, represented by the red star, sits in an underpopulated area of stellar parameter space as a massive, evolved subgiant.' (2019)Kepler 1658 b is a very special exoplanet.

It’s one of only a dozen or so whizzing around mildly-massive subgiant stars.

“…Kepler-1658 is a subgiant with Teff = 6216 ± 78 K, R? = 2.89 ± 0.12 R , and M?= 1.45 ± 0.06 M . As a massive subgiant, Kepler-1658 is currently undergoing a rapid phase of stellar evolution, joining only 9 known exoplanet hosts with similar properties (15 including statistically validated planets)….”
(“The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet“, Ashley Chontos et al., The Astronomical Journal (Submitted March 4, 2019))

That’s important for several reasons.

First, mid-sized stars on the Hertzsprung-Russell diagram’s subgiant branch are changing from main-sequence stars into red giants. The Hertzsprung-Russell diagram is a brightness-mass diagram developed in the early 20th century.

Back to mid-sized stars. They’re in the subgiant transitional stage for a only short time. Short on a cosmic scale, that is. A few million years isn’t much, compared to the 13,787,000,000 years since this universe started.10

Stars that are a bit more massive than ours, in this transitional stage, and have massive planets in tight orbits — like I said, we’ve only spotted maybe a dozen or so.

A Star’s Spin

'The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet Detection,' Ashley Chontos et al. - 'Figure 4. Top: Transit-clipped Quarter 11 long-cadence light curve for Kepler-1658. Bottom: Lomb-Scargle periodogram showing a strong peak at 5.66 ± 0.31 days, which we interpret as the stellar rotation period.' (2019)Kepler-1658 b’s star may be an oddball, too.

Ashley Chontos and her team didn’t have all that much data to work with — Kepler-1658b is a bit over 2,600 light-years away.

So they used mathematical tools like the Lomb-Scargle Periodogram to make sense of what they did have.

Lomb-Scargle Periodograms let researchers detect periodicity in unevenly-sampled data sets. Its generic name is least-squares spectral analysis; and it’s also callled the Vaníček method, Gauss-Vaniček method and Lomb method. None of which matters much in everyday life.

The point is that Kepler-1658 b’s star (probably) rotates ever five and two thirds days. That’s fairly fast, certainly compered to our sun’s leisurely 25 and spare change equatorial rotation period.

My memory tells me that at least a few ‘how planetary systems form’ ideas said that planets wouldn’t happen around fast-rotating stars.

It had something to do with angular momentum. Which, the last I checked, scientists still weren’t sure about when it came to how it got distributed between a star and its planets.11

Dealing With Data, Accepting New Knowledge

B. Saxton (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)'s infrared image of Elias 2-27's protoplanetary diak. (2018)
Planetary systems under construction: dusty discs surrounding nearby young stars. (2018)

I’ll occasionally get asked ‘how can scientists know how…’ stars form, old the universe is, and so on.

The short answer is, they don’t.

Not the way I can know that a plant grows from a seed.

Most seeds grow into plants in a matter of weeks or months. I can know that a seed grows into a plant by sticking it in soil and checking its progress every day or so.

Maybe somewhere in this galaxy, or in another, there are folks who live longer than we do. And have watched clouds of gas and dust condense into stars and planets.

Or at least have records spanning millions of years, the way we have an archive going back a few thousand.

Right now, we’re stuck with observing our part of this galaxy; and comparing recent data with what’s been recorded since we started keeping track of stars and planets.

Where things like protoplanetary disks are in play, previous records don’t go back more than a few decades. It’s only recently that we’ve had telescopes and other tools that let us see that sort of detail.

The good news is that we can see a very great many stars: big, small, new, old, and almost everything in between.

We can’t observe a single molecular cloud collapse into stars and planets.12 But we can spot examples of the process in various stages of development.

Distant Stars, Pixels and Making Sense

'The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet Detection,' Ashley Chontos et al. - 'Figure 6. Panel (a): Target pixel files of Kepler-1658 averaged over one full quarter. Panel (b): A difference image using frames coinciding with the maxima and minima of a phase curve calculated from the measured rotation period. The star marks the location of Kepler-1658, and the companion identified using AO imaging is marked with a cross.' (2019)Now, about Kepler-1658 b: we don’t have sharp images of that star and planet.

At 2,600-plus light-years, we’re doing well to get the data we do have.

Making the job harder, there’s another star in Earth’s sky that’s about one Kepler-pixel away from Kepler-1658.

I’m running short on time, so here’s how Ashley Chontos and all explained what they did:

“…To create the difference image, we subtracted the data around the troughs from the data around the peaks. We did this for each pixel, creating a difference image which gives an indication of the relative strength of the rotational signal over the postage stamp. We then compared the difference image to an average image from the same observing quarter (Figure 6), and found that in 11 of the 17 quarters the pixel with the brightest flux is the same as the pixel where the rotational signal is the strongest….”
(“The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet“, Ashley Chontos et al., The Astronomical Journal (Submitted March 4, 2019))

Since I have free will — and that’s yet another topic — I could decide that I won’t believe Ashley Chontos and other scientists.

Depending on which flavor of crackpottyness I picked, I could insist that astronomy was a government plot to enslave us all. Or a Satanic snare, because there’s no mention of exoplanets in the Bible.

Or something else, equally imaginative and running counter to what we’ve been learning about this universe.

But that doesn’t make sense. Not to me.

Paying Attention, Pursuing Truth

Roger Sinnott, Rick Fienberg's IAU /Sky and Telescope magazine sky map: Cygnus. (June 5, 2011)Wrapping up for the week: You can’t see Kepler 1658 without a very, very good telescope.

But it’s in a familiar constellation, Cygnus; a bit south of a line between Gamma Cygni and Vega, and about a third of the way over from Gamma Cygni.

Gamma Cygni’s name, one of them, is Sadr. Like many star names, it’s from Arabic, and transliteration being what it is, also spelled Sador and Sadir in my language.

Gamma Cygni/Sadr is at the intersection of my culture’s Northern Cross, an asterism; or it’s between Cygnus the swan’s wingtips.

At least one team of scientists has been paying attention to Kepler-1658 and its hot Jupiter; learning more about stars, planets, tides and physics in the process.

“…As the first evolved system with detected inspiral, Kepler-1658 is a new benchmark for understanding tidal physics at the end of the planetary life cycle….”
(“The Possible Tidal Demise of Kepler’s First Planetary System“, Shreyas Vissapragada, Ashley Chontos, et al.; The Astronomical Journal (December 19, 2022))

One point the team made is that Kepler-1658 b is, or seems to be, brighter that expected when it’s passing behind its sun — from Earth’s viewpoint.

That’s unusual, particularly for a hot Jupiter. KOI-1.01, the hot Jupiter I dubbed “Dunkelheim”, for example, is the darkest known exoplanet.

Shreyas Vissapragada et al. suggest that Kepler-1658 b is glowing, thanks to tidal heating plus its star-hugging orbit.

That makes sense. We’ve known about tidal heating — heat coming from a planet or satellite getting flexed as it changes distance from its star or planet. And Kepler-1658 b has a slightly eccentric orbit.

And I’m sure we’ll learn a great deal more by studying Kepler-1658 b. Maybe the knowledge won’t end world hunger or let the Cubs win the World Series again.13

But I think paying attention to the world around us is a good idea. Even if it doesn’t have an immediate dollars-and-cents payoff.

Putting This Universe in Perspective

Hubble/ESA's image: NGC 4848 and other galaxies. (2020)
NGC 4848 and other galaxies. Wisdom 11:22

I don’t have to take notice of what’s around me, or keep up with some of what we’re learning about this wonder-packed universe.

But again: I think it’s a good idea. And I’m far from the first person who thought so.

Question the beauty of the earth, question the beauty of the sea, question the beauty of the air…. They all answer you, ‘Here we are, look; we’re beautiful.’…
“…So in this way they arrived at a knowledge of the god who made things, through the things which he made.”
(Sermon 241, St. Augustine of Hippo (ca. 411) [emphasis mine])

“Indeed, before you the whole universe is like a grain from a balance,
or a drop of morning dew come down upon the earth.
“But you have mercy on all, because you can do all things;
and you overlook sins for the sake of repentance.”
(Wisdom 11:2223 [emphasis mine])

My interest in the beauties and wonders surrounding us connects with my opinion that pursuing truth is a good idea. None of which interferes with my faith.

If we’re doing it right,pursuing truth and beauty will lead us to God. (Catechism of the Catholic Church, 27, 31-35, 74)

That’s because all truth points toward God. Showing an interest in God’s creation and taking God seriously makes sense. (Catechism, 27, 31-35, 41, 74, 282-289, 293-294, 1723, 2294, 2500)

I’ve talked about that before. Rather often:

1 Catalogs and strange worlds:

2 Kepler-1658 b’s story, in very brief:

3 Learning where planets come from:

4 An expanding exoplanet frontier:

5 (Not) just like home:

6 Still not just like home:

7 Current best models for how planets and stars form:

8 Some geek-speak:

9 Some of why Kepler-1658 b matters:

10 Stars, the universe and a sense of scale:

11 Aren’t you glad there won’t be a test on this?

12 Seeds, clouds and history:

13 Wrapping it up for the week; Cygnus, the Chicago Cubs, stars and physics:

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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.
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