18-hour year planet on edge of destruction

Astronomers from the University of Warwick have observed an exoplanet orbiting a star in just over 18 hours, the shortest orbital period ever observed for a planet of its type.

University of Warwick

This is an artist's impression of a hot Jupiter orbiting close to a star. Credit: University of Warwick/Mark Garlick
This is an artist’s impression of a hot Jupiter orbiting close to a star. Credit: University of Warwick/Mark Garlick

Astronomers from the University of Warwick have observed an exoplanet orbiting a star in just over 18 hours, the shortest orbital period ever observed for a planet of its type.

It means that a single year for this hot Jupiter – a gas giant similar in size and composition to Jupiter in our own solar system – passes in less than a day of Earth time.

The discovery is detailed in a new paper published today (20 February) for the Monthly Notices of the Royal Astronomical Society and the scientists believe that it may help to solve a mystery of whether or not such planets are in the process of spiralling towards their suns to their destruction.

The planet NGTS-10b was discovered around 1000 light years away from Earth as part of the Next-Generation Transit Survey (NGTS), an exoplanet survey based in Chile that aims to discover planets down to the size of Neptune using the transit method. This involves observing stars for a telltale dip in brightness that indicates that a planet has passed in front of it.

At any one time the survey observes 100 square degrees of sky which includes around 100,000 stars. Out of those 100,000 stars this one caught the astronomers’ eye due to the very frequent dips in the star’s light caused by the planet’s rapid orbit.

Lead author Dr James McCormac from the University of Warwick Department of Physics said: “We’re excited to announce the discovery of NGTS-10b, an extremely short period Jupiter-sized planet orbiting a star not too dissimilar from our Sun. We are also pleased that NGTS continues to push the boundaries in ground-based transiting exoplanet science through the discovery of rare classes of exoplanets.

“Although in theory hot Jupiters with short orbital periods (less than 24 hours) are the easiest to detect due to their large size and frequent transits, they have proven to be extremely rare. Of the hundreds of hot Jupiters currently known there are only seven that have an orbital period of less than one day.”

NGTS-10b orbits so rapidly because it is very close to its sun – only twice the diameter of the star which, in the context of our solar system, would locate it 27 times closer than Mercury is to our own Sun. The scientists have noted that it is perilously close to the point that tidal forces from the star would eventually tear the planet apart.

The planet is likely tidally locked so one side of the planet is constantly facing the star and constantly hot – the astronomers estimate the average temperature to be more than 1000 degrees Celsius. The star itself is around 70% the radius of our Sun and 1000 degrees cooler. NGTS-10b is also an excellent candidate for atmospheric characterisation with the upcoming James Webb Space Telescope.

Using transit photometry, the scientists know that the planet is 20% bigger than our Jupiter and just over twice the mass according to radial velocity measurements, caught at a convenient point in its lifecycle to help answer questions about the evolution of such planets.

Massive planets typically form far away from the star and then migrate either through interactions with the disc while the planet is still forming, or from interactions with additional planets much further out later in their life. The astronomers plan to apply for time to get high-precision measurements of NGTS-10b, and to continue observing it over the next decade to determine whether this planet will remain in this orbit for some time to come – or will spiral into the star to its death.

Co-author Dr David Brown adds: “It’s thought that these ultra-short planets migrate in from the outer reaches of their solar systems and are eventually consumed or disrupted by the star. We are either very lucky to catch them in this short period orbit, or the processes by which the planet migrates into the star are less efficient than we imagine, in which case it can live in this configuration for a longer period of time.”

Co-author Dr Daniel Bayliss said: “Over the next ten years, it might be possible to see this planet spiralling in. We’ll be able to use NGTS to monitor this over a decade. If we could see the orbital period start to decrease and the planet start to spiral in, that would tell us a lot about the structure of the planet that we don’t know yet.

“Everything that we know about planet formation tells us that planets and stars form at the same time. The best model that we’ve got suggests that the star is about ten billion years old and we’d assume that the planet is too. Either we are seeing it in the last stages of its life, or somehow it’s able to live here longer than it should.”

NGTS is situated at the European Southern Observatory’s Paranal Observatory in the heart of the Atacama Desert, Chile. It is a collaboration between UK Universities Warwick, Leicester, Cambridge, and Queen’s University Belfast, together with Observatoire de Genève, DLR Berlin and Universidad de Chile. In the UK, the facility and the research is supported by the Science and Technologies Facilities Council (STFC) part of UK Research and Innovation (UKRI).


* ‘NGTS-10b: The shortest period hot Jupiter yet discovered’ is published in Monthly Notices of the Royal Astronomical Society, DOI: 10.1093/mnras/staa115

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Ron Long
February 23, 2020 2:55 am

1,000 deg C? Jupiter is a gas giant, mostly hydrogen and helium, but probably with a rocky core. How does a gas giant retain gas this close to a star? Wouldn’t you think the solar winds would tear into it? At 1,000 deg C most rock types melt so NGTS-10B is not a good place to be for any conventional life forms, and there aren’t any politicians that can stand the heat anymore, so probably uninhabited. Have you noticed that astronomers are giddy about death watches, first Betelgeuse and now NGTS-10B?

Reply to  Ron Long
February 23, 2020 3:39 am

It is assumed that the Jupiter’s core is mostly liquid metallic hydrogen and helium.

Ron Long
Reply to  Vuk
February 23, 2020 6:07 am

Vuk, you are correct that it is presumed that Jupiter’s core is mostly liquid metallic hydrogen and helium, however, it also appears to be a common assumption that there is a iron-containing “rocky” central core. For those of you who like phrases like “zonal harmonics in gravity” and “plasma phase transition” you might check out: Understanding Jupiter’s Interior, by Militzer, et al, 2016, an excellent article that utilizes both satellite visits from Pioneer, Voyager, and Galileo projects, but also a lot of experimental data and, yes, some modelling. I don’t do modelling myself as prancing around in Calvin Klein underwear doesn’t work for me.

Reply to  Vuk
February 23, 2020 7:49 am

If there was rocky material in the cloud that the planets formed from, then there is going to be rocky material inside Jupiter.

Reply to  Ron Long
February 24, 2020 3:28 am

1. Astronomers are, unlike obnoxious fifteen year old climate scientists, eight year olds at heart. Nothing is quite so impressive as an explosion. I can relate to this.

2. Yes, hot Jupiters do blow off matter from being so close and hot. That said, when dealing with gravity over 10x Earth’s, and a magnetosphere more powerful than that, the losses are at a pretty slow pace. I think that it will be swallowed by its parent star much sooner than it would take to burn away in orbit.

Samuel C Cogar
February 23, 2020 4:26 am

I would think that a “gas giant” planet such as NGTS-10b is, and orbiting a star such as it is, ….. should look more like a comet with a long, long tail …… because its gravity would not be able to hold onto it gaseous atmosphere at that orbital speed.

Reply to  Samuel C Cogar
February 23, 2020 7:52 am

Orbital speed has nothing to do with how well a planet holds onto it’s atmosphere.
What rips atmosphere from planets is solar wind.
A Jupiter like planet is likely to have a pretty strong magnetic field, which protects the atmosphere from the solar wind. However, at those distances the solar wind is pretty fierce as well.

Samuel C Cogar
Reply to  MarkW
February 23, 2020 12:10 pm

MarkW, ….. I am really curious, if planet NGTS-10b is orbiting its star in just over 18 hours, ….. just how fast (speed) is that planet travelling in its orbit?

If planet Mercury was orbiting our Sun in just over 18 hours ….. could we easily see it?

Reply to  Samuel C Cogar
February 23, 2020 11:06 am

I suspect that they don’t know squat about this hot Jupiter apart from its orbital period, nor for the half a dozen similar hot shadows they have seen so far.

Astronomy is now competing with archeology for how much hypothesis and conjecture you can spin from a grain of information and still pretend to be talking science.

Reply to  Samuel C Cogar
February 24, 2020 3:30 am

Universe Sandbox agrees.

February 23, 2020 4:39 am

I’m guessing that the unlit, ‘cold’, side would still be pretty darn hot due to very strong convection, similar to Venus. Venus is also tidally locked and has very high wind speeds which move the heat around. link Given the closeness of NGTS-10b to its sun and the resulting energy it receives, one would expect the winds to be much faster than those of Venus.

As a result of its winds, Venus is the same temperature day or night. I would expect the same of NGTS-10b.

Philip Mulholland
Reply to  commieBob
February 23, 2020 5:42 am


You do realise that you have just destroyed the basic premise of Climate Science >that it is daily surface rotation that distributes energy from the lit to the dark hemisphere of a planet?


Reply to  Philip Mulholland
February 23, 2020 6:07 am

This process of energy interception by the surface of the sunlit side, coupled with mass motion of heated air, and radiative cooling to space from the surface of the unlit side, is the diagnostic characteristic of a thermal Hadley cell.

This is a nomenclature quibble rather than one about physics. I always thought a Hadley cell moved heat from the equator towards one of the poles. Similarly, I thought zonal flows were responsible for moving heat from the lit side to the unlit side. Am I misunderstanding what you wrote?

It seems obvious that, absent planetary rotation, an atmosphere will still move heat from the lit side to the unlit side. Given the uniformity of the temperature on Venus, it also seems obvious that the process is efficient.

Philip Mulholland
Reply to  commieBob
February 23, 2020 6:56 am


Interesting quibble. The problem for me is to find a way of nailing the ridiculous nonsense that solar intensity is divided by 4. On a tidally locked planet divide by 4 for the solar input is impossible, so the whole basis of the cold Sun / cold Earth concept is shown up for the fake science that it actually is.
On Venus the Hadley cell extends from the equator to the pole. Have a look at the impact of the solar zenith on the Venusian atmosphere, it is effectively a blow torch heating point and this generates a bow shock wave as the planet rotates in sequence with its annual orbit.
On Earth however the rapid daily rotation means that the equatorial traverse of the solar zenith exceeds the speed of sound. Earth’s rapid motion carries the heated air round to the night side, where the tropopause drops down due to surface radiant cooling to space through the atmospheric window, hence this is a zonal flow effect. On Venus by contrast the zonal flow spirals all the way to the poles and so it wraps around itself and does both jobs (zonal & meridional).
The impact of Coriolis is fundamental to the process of creating a latitudinal limit to the extent of a Hadley cell.
(p.s. Thanks for taking the click bait, you have pushed me up to 900 views 😉 ).

Reply to  Philip Mulholland
February 23, 2020 7:33 am

Am I right in thinking that, on a tidally locked planet, coriolis doesn’t matter?

Philip Mulholland
Reply to  Philip Mulholland
February 23, 2020 7:48 am

“Am I right in thinking that, on a tidally locked planet, Coriolis doesn’t matter?”

That is the ultimate research question. I don’t know the answer. For an 18 hour year and an 18 hour day, I wonder if the Coriolis effect will be present in spades and so our original premise of a Venus atmosphere is the wrong model, and in fact the atmosphere would be banded like Jupiter on steroids.

Crispin in Waterloo
Reply to  Philip Mulholland
February 23, 2020 11:09 am

I am not sure why you guys think Venus is tidally locked. It has a retrograde rotation and the length of the day is ~117 Earth Days. The orbit is 224.65 Earth Days so there are (because of the reverse rotation) almost 2 Venusian days in a Venusian year. It therefore cannot be tidally locked.

In the past two days I have red that winds on Venus are very low speed and very high speed. The truth is that the winds whip the atmosphere around the planet every 4.8 (average) Earth days, meaning the atmosphere rotates 60 times faster than the planet it self. That is amazing. Further, the rotation speed of the atmosphere varies from orbit to orbit, 3.9 to 5.4 Earth days days. In general, it is speeding up. Must be caused by the Universal Explanation™ : human CO2 emissions.

Reply to  Philip Mulholland
February 23, 2020 11:41 am

Good point Crispin, I must admit the claim that Venus was tidally locked came as a surprise to me.

The sidereal day is 243 Earth days, longer than the venusian year but since retrograde the solar day is shorter at 117 Earth days.

Reply to  Philip Mulholland
February 23, 2020 4:08 pm

Venus is tidally locked with Earth, just as the Moon is. The Magellan project revealed this fact.

“The 584-day average interval between successive close approaches to Earth is almost exactly equal to 5 Venusian solar days,[114] but the hypothesis of a spin–orbit resonance with Earth has been discounted.” -Wikipedia

Sorry for the wiki thing, and they are wrong about the resonance, for which they referenced an article from 1979, before the Magellan data were obtained.

Tallbloke has an interesting article about Venus’ rotation rate slowing inexplicably:


Reply to  Philip Mulholland
February 23, 2020 5:41 pm

Crispin in Waterloo February 23, 2020 at 11:09 am

I am not sure why you guys think Venus is tidally locked.

The point is that almost no heat is transferred from the sunlit side of the planet to the dark side as a result of planetary rotation.

A problem is that wind velocity is defined relative to the planet’s surface. With low wind speed, all of Earth’s atmosphere is moved from the lit side to the dark side every day due to our rotation. Even with its relatively high wind speeds, Venus takes longer to move its atmosphere from the lit side to the dark side. In spite of that, convection seems to be quite efficient at moving heat from the lit side of Venus to its unlit side.

In terms of heat transfer, Venus is close enough to being tidally locked.

Crispin in Waterloo
Reply to  Philip Mulholland
February 23, 2020 7:38 pm


I think a complete description has to include the point that the atmosphere moves heat from the hot side to the cold side (all of it) on 2 days. If there were no wind, and it rotated at half the rate of Earth, the same would be accomplished.

This this reason alone I doubt that there is a functional difference. The atmosphere is rotating around the planet, and by definition is not a Hadley Cell which is latitudinal. I have no idea what makes the atmosphere rotate so rapidly. It is not even a stable rotation rate so something is both driving and moderating it between two limits – very interesting to me.

A note for WBWilson – you are referring to the beat frequency of the Venus-Earth-Moon system. You are correct about the frequency. It is visible on the surface of the sun in the patterns created by making “butterfly diagrams”. This demonstrates that the Earth-Moon + Venus barycentre have an effect on the sun’s surface because by locating it, you can show that it matches patterns in the tracks of sunspots. I was quite surprised when I read that because the planets are supposed to be “too small” to influence anything about the Sun.

Reply to  Philip Mulholland
February 23, 2020 11:41 pm

Crispin in Waterloo February 23, 2020 at 7:38 pm

… I have no idea what makes the atmosphere rotate so rapidly.

I thought convection was the obvious cause. What am I missing?

At the equator, the Earth and the atmosphere above it move at 460 m/s. Since we define wind relative to the surface, there’s not much wind. Relative to a point in space though, the air mass is moving really fast. It reminds me of a thermal wheel heat exchanger where one side predominantly receives energy from the sun and the other radiates it to space.

Philip Mulholland
Reply to  Philip Mulholland
February 24, 2020 4:20 am

“The atmosphere is rotating around the planet, and by definition is not a Hadley Cell which is latitudinal.”

As CommieBob points out, neither of us think that Venus is tidally locked, it is just that its slow retrograde rotation makes Venus the closest approximation to a tidally locked terrestrial planet with an atmosphere that we can directly observe.
With regards to the issue of a Hadley cell being a latitudinal (meridional) transport system, consider this point. Because the daily rotation rate of the Earth is so rapid the solar zenith point translates west through the equatorial atmosphere at circa 1,000 mph (its locus therefore exceeds the speed of sound).
Have a look at the Ventusky plot of the Pacific for 20 Mar 2019

and compare it with the WorldView image for the same date

Notice the pulsed nature of the ITCZ convection structure as the solar zenith races west, and the banded V formation of the cloud systems to the east of each ITCZ cell.
Compare this with Venus; the main difference for Venus is that there is only one solar zenith convection point on this slowly rotating planet. Are the North East & South East trade winds on Earth zonal or meridional systems? It seems to me that they are both.
On Venus the Coriolis effect is so weak that there is no latitudinal constraint on the polar advection of air at this planet’s tropopause, and the only place on Venus where the TOA air can return to the surface is at the two rotation poles of this planet.
On Earth however there are multiple solar zenith ITCZ convection cells and because the Coriolis effect limits the latitudinal reach of the advecting TOA air, our atmosphere breaks up into multiple surface anticyclonic cells in the Horse latitudes.

Reply to  commieBob
February 24, 2020 3:32 am

The ultra-reflective clouds help too.

February 23, 2020 5:16 am

Let that tipping point be a lesson to you all if you don’t change the climate now.

February 23, 2020 5:35 am

Down here at the ground level at 11 C degrees:
“The UK’s NHS is to ask patients with suspected coronavirus to drive to health centre car parks, with nurses in Hazmat gear swabbing them through a rolled-down window.
The scheme, being pioneered by a London trust, comes alongside the rollout of “home testing” for coronavirus – with nurses and doctors increasingly asked to visit patients at home to collect their samples. “

Reply to  Vuk
February 23, 2020 7:21 am

It seems like a little more thought could go into that.

Reply to  Scissor
February 23, 2020 11:45 am

It’s amazing that they don’t seem to have thought this through yet. It’s like an emergency hack solution to an unexpected problem. Not like they’ve had over 6 weeks to get their shit together before it hits UK.

Reply to  Greg
February 24, 2020 3:38 am

NHS is a bureaucracy before all else. Six years isn’t enough time.

Mark Luhman
Reply to  Vuk
February 23, 2020 8:13 am

Maybe if England did not relies on treating patent in what I call emergence room method they would not have this problem. Here in the US we have multi paths to see a Doctor, first is the primary care physician, next is the urgent care office, lastly the emergency room. When thing function here correctly there is never more than an handful of people in the waiting room, none are in it for more than an hour.

February 23, 2020 7:48 am

How do they know it’s a planet and not a sun spot?

Reply to  MarkW
February 23, 2020 11:14 am

because they are not looking for sun spots 😉

Steve Reddish
Reply to  MarkW
February 23, 2020 3:58 pm

I like Greg’s answer, but also imagine that 18 hours is too brief for a solar rotation period.


Reply to  MarkW
February 24, 2020 3:42 am

Size, intensity differential, spectrum, and sustained period come to mind.

February 23, 2020 8:11 am

An extreme example of the term ‘global warming’, with not a hint of ‘anthropogenic’ in sight. Doesn’t fit the narrative. Fake news.

Tom Abbott
February 23, 2020 8:26 am

Is it inevitable that Jupiter-type planets spiral into the star they orbit?

I suppose the lifetime of the star would have a lot to do with it.

Reply to  Tom Abbott
February 23, 2020 1:22 pm

According to current theory, it is. The only reason why our Jupiter didn’t is because of the influence of Saturn.

Reply to  MarkW
February 24, 2020 3:49 am

One of them. Others now suggest that a bigger one did migrate inward, pushing Jupiter outward in the process, then either was swallowed up or torn apart in order to form the inner planets.

Yet another suggests that Mercury is the burned-out husk of one.

Reply to  Tom Abbott
February 24, 2020 3:46 am

There’s lots of variables, many of which multiply as a planet grows bigger.

Let’s just say that the early part of a solar system’s formation is pretty chaotic.

Jeff Alberts
February 23, 2020 5:10 pm

“Astronomers from the University of Warwick have observed an exoplanet orbiting a star in just over 18 hours, the shortest orbital period ever observed for a planet of its type.”

Observed it?

Reply to  Jeff Alberts
February 24, 2020 3:53 am

Either by passing in front of the star, blocking and refracting light, or by detecting a wobble in the star itself. There’s a couple of other more exotic methods, but these are the two most common.

February 23, 2020 6:21 pm

I have been saying the same since they started observing these ‘transits’. It is not planets being observed it is some other phemonena. An 18 hour orbit is ridiculous.

Reply to  Muontau
February 24, 2020 3:54 am

Space is a ridiculous place.

Steve Z
February 24, 2020 4:41 pm

In our own solar system, the moon is at about the same distance from the sun as Earth, and receives about the same solar radiation, but the moon has no atmosphere, because its weaker gravity cannot prevent gases from escaping, while Earth’s stronger gravity can hold its atmosphere.

If this exoplanet has twice the mass of Jupiter but circles its star in only 18 hours, its “bright side” is probably too hot to hold an atmosphere, while the dark side could have an atmosphere held in by the planet’s strong gravity. If this planet is “tidally locked” with the same side always facing the star, there would probably be strong winds along the “twilight zone” between day and night, where gases from the dark side could be heated by the star, then rise away from the planet due to thermal expansion, and possibly the dark-side atmosphere could be depleted by this mechanism.

The article mentions the possibility that tidal forces could tear the planet apart, but the gravity of such a massive planet at such a short distance from the star also could cause disruptions in the star, with the side facing the planet bulging out toward the planet, and this “bulge” in the star could actually rotate at the same angular speed as the planet.

It will be interesting to see whether this planet is in the final stages of orbital decay, and will eventually be absorbed into the star, possibly with a massive explosion.

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