Hubble finds far-away planet vanishing at record speed

December 13, 2018, Johns Hopkins University
This artist’s illustration shows a giant cloud of hydrogen streaming off a warm, Neptune-sized planet just 97 light-years from Earth. The exoplanet is tiny compared to its star, a red dwarf named GJ 3470. The star’s intense radiation is heating the hydrogen in the planet’s upper atmosphere to a point where it escapes into space. The alien world is losing hydrogen at a rate 100 times faster than a previously observed warm Neptune whose atmosphere is also evaporating away. Credit: NASA, ESA, and D. Player (STScI)

The speed and distance at which planets orbit their respective blazing stars can determine each planet's fate—whether the planet remains a longstanding part of its solar system or evaporates into the universe's dark graveyard more quickly.

In their quest to learn more about far-away beyond our own solar system, astronomers discovered that a medium-sized planet roughly the size of Neptune, GJ 3470b, is evaporating at a rate 100 times faster than a previously discovered planet of similar size, GJ 436b.

The findings, published today in the journal of Astronomy & Astrophysics, advance astronomers' knowledge about how planets evolve.

"This is the smoking gun that planets can lose a significant fraction of their entire mass. GJ 3470b is losing more of its mass than any other planet we seen so far; in only a few billion years from now, half of the planet may be gone," said David Sing, Bloomberg Distinguished Professor at Johns Hopkins and an author on the study.

The study is part of the Panchromatic Comparative Exoplanet Treasury (PanCET) program, led by Sing, which aims to measure the atmospheres of 20 exoplanets in ultraviolet, optical and , as they orbit their stars. PanCET is the largest exoplanet observation program to be run with NASA's Hubble Space Telescope.

One particular issue of interest to astronomers is how planets lose their mass through evaporation. Planets such as "super" Earths and "hot" Jupiters orbit more closely to their stars and are therefore hotter, causing the outermost layer of their atmospheres to be blown away by evaporation.

This graphic plots exoplanets based on their size and distance from their star. Each dot represents an exoplanet. Planets the size of Jupiter (located at the top of the graphic) and planets the size of Earth and so-called super-Earths (at the bottom) are found both close and far from their star. But planets the size of Neptune (in the middle of the plot) are scarce close to their star. This so-called desert of hot Neptunes shows that such alien worlds are rare, or, they were plentiful at one time, but have since disappeared. The detection that GJ 3470b, a warm Neptune at the border of the desert, is fast losing its atmosphere suggests that hotter Neptunes may have eroded down to smaller, rocky super-Earths. Credit: NASA, ESA, and A. Feild (STScI)

While these larger Jupiter-sized and smaller Earth-sized exoplanets are plentiful, medium Neptune-sized exoplanets (roughly four times larger than Earth) are rare. Researchers hypothesize that these Neptunes get stripped of their atmospheres and ultimately become smaller planets. It's difficult, however, to actively witness them doing so because they can only be studied in UV light, which limits researchers to examining nearby no greater than 150 light-years away from earth, not obscured by interstellar material. GJ 3470b is 96 light-years away and circles a red dwarf star in the general direction of the constellation Cancer.

In this study, Hubble found that exoplanet GJ 3470b had lost significantly more mass and had a noticeably smaller exosphere than the first Neptune-sized studied, GJ 436b, due to its lower density and receipt of a stronger radiation blast from its .

GJ 3470b's lower density makes it unable to gravitationally hang on to the heated atmosphere, and while the star hosting GJ 436b was between 4 billion and 8 billion years old, the star hosting GJ 3470b is only 2 billion years old; a younger star is more active and powerful, and, therefore, has more radiation to heat the planet's atmosphere.

Sing's team estimates that GJ 3470b may have already lost up to 35 percent of its total mass and, in a few billion years, all of its gas may be stripped off, leaving behind only a rocky core.

"We're starting to better understand how planets are shaped and what properties influence their overall makeup," Sing said. "Our goal with this study and the overarching PanCET program is to take a broad look at these planets' atmospheres to determine how each planet is affected by its own environment. By comparing different planets, we can start piecing together the larger picture in how they evolve."

Looking forward, Sing and the team hope to study more exoplanets by searching for helium in infrared light, which will allow a greater search range than searching for hydrogen in UV light.

Currently, planets, which are made largely of hydrogen and helium, can only be studied through tracing hydrogen in UV light. Using Hubble, the upcoming NASA James Webb Space Telescope (which will have a greater sensitivity to helium), and a new instrument called Carmenes that Sing recently found can precisely track the trajectory of helium atoms, astronomers will be able to broaden their pursuit of distant planets.

Explore further: An exoplanet loses its atmosphere in the form of a tail

More information: V. Bourrier et al. Hubble PanCET: an extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470b, Astronomy & Astrophysics (2018). DOI: 10.1051/0004-6361/201833675

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rrwillsj
not rated yet Dec 13, 2018
Leaves me wondering what happens to the lost gases?
Captured by it's host star, to increase it's mass?
Expelled out of the star system into Interstellar Space?
Collected by other bodies in that system?
Something else, still to be determined?
All of the above?
Whydening Gyre
not rated yet Dec 13, 2018
I couldn't find out how close this (or the other mentioned) actually orbits it's star...
Maybe it's my dys'left'ic eyes...
Onathan
5 / 5 (1) Dec 13, 2018
Might there be any rocky cores of stripped Neptunes in our system?
Ojorf
3.7 / 5 (3) Dec 13, 2018
I couldn't find out how close this (or the other mentioned) actually orbits it's star...
Maybe it's my dys'left'ic eyes...


Bottom axis of the graphic. It's logarithmic.
RNP
5 / 5 (5) Dec 14, 2018
@Whydening Gyre
GJ3470 is at a distance of 0.031 AU .GJ436b is at a similar distance of 0.028 AU (N.B. these are semi-major axes, but eccentricities are low).

You can get more details about each of the planets here;
https://en.wikipe...e_3470_b
Da Schneib
3.7 / 5 (3) Dec 14, 2018
Might there be any rocky cores of stripped Neptunes in our system?
Not inside the Kuiper Belt (inside 20 light hours). Just like Tombaugh discovered Pluto. You can do that stuff with metal vernier gauges. You don't even need electronics. Just gotta be precise enough with the verniers.
Da Schneib
3.7 / 5 (3) Dec 14, 2018
Back before there were electronic gauges, or computer numeric readouts, there were verniers. I have done successful astrophotography with vernier mounts. https://en.wikipe...er_scale
Mark Thomas
5 / 5 (1) Dec 14, 2018
I have done successful astrophotography with vernier mounts


Thanks Da Schneib! My computerized/motorized telescope does not have a Vernier scale on the right ascension or declination markings, but now I have a idea how they are used to achieve greater precision on certain telescopes.
Mark Thomas
5 / 5 (2) Dec 14, 2018
Might there be any rocky cores of stripped Neptunes in our system?


Da Schneib is correct, but if you were similarly interested in a likely exposed protoplanet core (or fragment), take a look at 16 Psyche. NASA is launching an orbiter there in 2022, with a Mars gravity assist in 2023 and arriving in 2026. I think the exploration of 16 Psyche is going to be mind-blowing for a lot of people and may help to stir interest in asteroid mining.

https://en.wikipe...6_Psyche
Da Schneib
3.7 / 5 (3) Dec 14, 2018
I have done successful astrophotography with vernier mounts


Thanks Da Schneib! My computerized/motorized telescope does not have a Vernier scale on the right ascension or declination markings, but now I have a idea how they are used to achieve greater precision on certain telescopes.
Reading and setting verniers used to be an important skill for an engineer. They're still used some places. One nice thing about them is that they don't depend on electronics, so if the power goes out, they still work.
rrwillsj
3.7 / 5 (3) Dec 14, 2018
Yeah? But if the power foes out? I'm gonna hafta squint real hard!

jeebus! MT & DS, you just brought back some fond memories of when I was a snot-nosed kid using a slide ruler.

Thanks guys!
wduckss
5 / 5 (1) Dec 14, 2018
About what they maunder (authors)???

Mass up to 15 MJ/(vs) Mass above 15 M

Brown dwarf (planets)….Mass of Jup….Temperature °K….Planets orbit AU

DH Tauri b…………………..12………………….2.750…………………330
ULAS J133553.45+1…….15 _31………..500 -550

2MASS J2126-8140…….13,3…………. 1.800…………………..6.900
Gliese 570…………………~50…………..750 – 800……………1.500

Mass vs Mass
2M 044144………………9.8±1.8……..1.800 ……………………15 ± 0.6
DT Virginis……………….8.5 ± 2.5……695±60…………………….1.168

Teide 1…………………….57± 15……2.600±150
Epsilon Indi Ba, Bb…......40 – 60 .........1.300-1400 (880-940)......1.500

B Tauri FU……………..15………………2.375……………….......…700
DENIS J081730.0……15…………………950
Da Schneib
3 / 5 (2) Dec 14, 2018
@rrwillsj, I thought of the slide rule I found in my dad's stuff and learned to use when I was a kid myself. Dad was impressed and got me my first calculator that Christmas, and I never looked back. I wasn't limited to three or four sig figs any more!
rrwillsj
3.7 / 5 (3) Dec 14, 2018
"... I wasn't limited to three or four sig figs any more! ..."

Yeah, Texas Instruments rocked!

Though for some strange reason?
I continued to make the same errors in my calcs!

{shake my head with rueful grin}
aykev
5 / 5 (3) Dec 15, 2018
I'd like to point out an issue in the article. The paragraph right after the figure states:

> [...] medium Neptune-sized exoplanets (roughly four times larger than Earth) are rare.

This threw me off for a second since Neptune isn't four times larger than Earth, until I realized it was as measured by radius. I would suggest changing the wording to reflect that, to something like:

> [...] medium Neptune-sized exoplanets (those with a radius roughly four times larger than that of Earth) are rare.

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