̽��ֱ�� of Cambridge - Ed Gillen

Astronomers discover the first ‘ultrahot Neptune’: one of nature’s improbable planets

Anonymous — Mon, 21 Sep 2020 13:25:16 +0000

̽��ֱ��planet orbits so close to its star that its year lasts only 19 hours, and stellar radiation heats the planet to over 1700 degrees Celsius.

At these temperatures, heavy elements like iron can be ionised in the atmosphere and molecules disassociated, providing a unique laboratory to study the chemistry of planets outside the solar system.

Although the planet weighs twice as much as Neptune, it is also slightly larger and has a similar density. Therefore, LTT 9779b should have a huge core of around 28 Earth masses, and an atmosphere that makes up around 9% of the total planetary mass.

̽��ֱ��system itself is around two billion years old, and given the intense irradiation, a Neptune-like planet would not be expected to keep its atmosphere for so long, providing a puzzle for astronomers to solve; how such an improbable system came to be. ̽��ֱ��results are reported in the journal Nature Astronomy.

LTT 9779 is a Sun-like star located at a distance of 260 light years, a stone’s throw in astronomical terms. It is metal-rich, having twice the amount of iron in its atmosphere than the Sun. This could be a key indicator that the planet was originally a much larger gas giant, since these bodies tend to form close to stars with the highest iron abundances.

Initial indications of the existence of the planet were made using the Transiting Exoplanet Survey Satellite (TESS), as part of its mission to discover small transiting planets orbiting nearby and bright stars across the whole sky. Such transits are found when a planet passes directly in front of its parent star, blocking some of the starlight, and the amount of light blocked reveals the companion’s size. Planets like these, once fully confirmed, can allow astronomers to investigate their atmospheres, providing a deeper understanding of planet formation and evolution processes.

̽��ֱ��transit signal was confirmed in early November 2018 as originating from a planetary mass body, using observations taken at the ESO la Silla Observatory in northern Chile. HARPS uses the Doppler Wobble method to measure planet masses and orbital characteristics. When objects are found to transit, Doppler measurements can be organized to confirm the planetary nature in an efficient manner. In the case of LTT 9779b, the team were able to confirm the planet’s existence after only one week of observations.

Professor James Jenkins from the Department of Astronomy at the Universidad de Chile, who led the team, said: “ ̽��ֱ��discovery of LTT 9779b so early in the TESS mission was a complete surprise; a gamble that paid off. ̽��ֱ��majority of transit events with periods less than one day turnout to be false-positives, normally background eclipsing binary stars.”

̽��ֱ��planet was uncovered in only the second of 26 sectors of observations that TESS would be observing across the whole sky. Since no similar types of planets were detected in the TESS precursor missions Kepler and K2, the finding was even more exciting.

“We selected this candidate from a TESS alert due to its very short orbital period. After inspecting the light curve, we found it was a good candidate for an upcoming week-long observation campaign using the HARPS spectrograph in La Silla,” said co-author Matías Díaz, also from the Universidad de Chile. “We planned the observations carefully, to maximize the use of the spectrograph and sample the orbit of the candidate in an optimal way. During the first nights of data we saw the observations matched the predicted period of the candidate. Further analysis of the seven nights of observations in November were consistent with a massive Neptune planet.”

LTT 9779b exists in the ‘Neptunian Desert’, a region devoid of planets when we look at the population of planetary masses and sizes. Although icy giants seem to be a fairly common by-product of the planet formation process, this is not the case very close to their stars. ̽��ֱ��researchers believe these planets get stripped of their atmospheres over cosmic time, ending up as so-called Ultra Short Period planets.

̽��ֱ��Kepler mission found that Ultra Short Period planets, those that orbit their stars in one day or less, come mainly in the form of large gas giants or small rocky planets. Models tell us that planets like LTT 9779b should be stripped of their atmospheres through a process called photoevaporation as they move close to their stars. ̽��ֱ��large gas giants, on the other hand, have strong gravitational fields that can hold onto their atmospheres, and so we end up with a dearth of planets like Neptune with the shortest orbital periods.

“Planetary structure models tell us that the planet is a giant core dominated world, but crucially, there should exist two to three Earth-masses of atmospheric gas,” said Jenkins. “But if the star is so old, why does any atmosphere exist at all? Well, if LTT 9779b started life as a gas giant, then a process called Roche Lobe Overflow could have transferred significant amounts of the atmospheric gas onto the star.”

Roche Lobe Overflow is a process whereby a planet comes so close to its star that the star’s stronger gravity can capture the outer layers of the planet, causing it to transfer onto the star and so significantly decreasing the mass of the planet. Models predict outcomes similar to that of the LTT 9779 system, but they also require some fine-tuning.

“It could also be that LTT 9779b arrived at its current orbit quite late in the day, and so hasn’t had time to be stripped of the atmosphere. Collisions with other planets in the system could have thrown it inwards towards the star. Indeed, since it is such a unique and rare world, more exotic scenarios may be plausible,” said Jenkins.

Members of the Cambridge Astronomy department are part of the Next-Generation Transit Survey (NGTS). ̽��ֱ��NGTS team conducted follow-up observations of LT9779b’s transit to help confirm the planetary nature of the system and better constrain its properties.

“LTT 9779b is an intriguing planet, being the first of its kind discovered,” said co-author Dr Ed Gillen, from Cambridge’s Cavendish Laboratory. “It is particularly exciting because of its peculiarity: how did this planet come to arrive on such a short period orbit and why does it still possess an atmosphere? Fortunately, the planetary system is located nearby so we can study it in detail, which promises new insights into how such planets come to be and what they are made of.”

Reference:
James S. Jenkins et al. ‘An ultrahot Neptune in the Neptune desert.’ Nature Astronomy (2020). DOI: 10.1038/s41550-020-1142-z

Adapted from a Universidad de Chile press release.

An international team of astronomers, including researchers from the ̽��ֱ�� of Cambridge, has discovered a new class of planet, an ‘ultrahot Neptune’, orbiting the nearby star LTT 9779.

This planet is particularly exciting because of its peculiarity: how did this planet come to arrive on such a short period orbit and why does it still possess an atmosphere?

Ed Gillen

icardo Ramirez, Universidad de Chile

Artist's impression of LTT 9779b

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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‘Lost’ world’s rediscovery is step towards finding habitable planets

sc604 — Tue, 21 Jul 2020 07:39:47 +0000

̽��ֱ��planet, the size and mass of Saturn with an orbit of thirty-five days, is among hundreds of ‘lost’ worlds that astronomers, including from the ̽��ֱ�� of Cambridge, are using new techniques to track down and characterise, in the hope of finding cooler planets like those in our solar system, and even potentially habitable planets.

Reported in Astrophysical Journal Letters, the planet named NGTS-11b orbits a star 620 light-years away and is located five times closer to its sun than Earth is to our own.

̽��ֱ��planet was originally found in a search for planets in 2018 by the ̽��ֱ�� of Warwick-led team using data from NASA’s TESS telescope. This uses the transit method to spot planets, scanning for the tell-tale dip in light from the star that indicates that an object has passed between the telescope and the star.

However, TESS only scans most sections of the sky for 27 days. This means many of the longer period planets only transit once in the TESS data: without a second observation the planet is effectively lost. Researchers from Cambridge’s Cavendish Laboratory are part of the Next-Generation Transit Survey (NGTS) team which, after identifying a single transit event in the TESS data of the star NGTS-11, monitored the system in search of additional transits to confirm the planetary nature of the transiting object.

“By chasing that second transit down we’ve found a longer period planet. It’s the first of hopefully many such finds pushing to longer periods,” said lead author Dr Samuel Gill from the ̽��ֱ�� of Warwick. “These discoveries are rare but important, since they allow us to find longer period planets than other astronomers are finding. Longer period planets are cooler, more like the planets in our own solar system.”

NGTS-11b has a temperature of only 160°C – cooler than Mercury or Venus. Although this is still too hot to support life as we know it, it is closer to the Goldilocks zone than many previously discovered planets which typically have temperatures above 1000°C. ̽��ֱ��Goldilocks zone refers to a range of orbits that would allow a planet or moon to support liquid water: too close to its star and it will be too hot, but too far away and it will be too cold.

“While we have discovered many planets that orbit close to their host star, we know of fewer at longer periods and cooler temperatures, which makes NGTS-11b an interesting find that takes us one step closer to finding planets in the Goldilocks zone,” said co-author Dr Ed Gillen from Cambridge’s Cavendish Laboratory. “Longer period planets like NGTS-11b may help us to better understand the various evolutionary processes that planetary systems undergo both during and after their formation.”

NGTS has twelve state-of-the-art telescopes at its site in Chile, which means that researchers can monitor multiple stars for months on end, searching for lost planets. ̽��ֱ��dip in light from NGTS-11b is only 1% deep and occurs only once every 35 days, putting it out of reach of other telescopes.

There are hundreds of single transits detected by TESS that researchers will be monitoring using this method. This will allow them to discover cooler exoplanets of all sizes, including planets more like those in our own solar system. Some of these will be small rocky planets in the Goldilocks zone that are cool enough to host liquid water oceans and potentially extra-terrestrial life.

̽��ֱ��research was supported by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).

Reference:
Samuel Gill et al. ‘NGTS-11 b (TOI-1847 b): A Transiting Warm Saturn Recovered from a TESS Single-transit Event.’ ̽��ֱ��Astrophysical Journal Letters (2020). DOI: 10.3847/2041-8213/ab9eb9

Adapted from a ̽��ֱ�� of Warwick press release.

̽��ֱ��rediscovery of a lost planet could pave the way for the detection of a world within the habitable ‘Goldilocks zone’ in a distant solar system.

NGTS-11b is an interesting find that takes us one step closer to finding planets in the Goldilocks zone

Ed Gillen

Y. Beletsky (LCO)/ESO

Paranal nights

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‘Forbidden’ planet found wandering ‘Neptunian Desert’

sc604 — Wed, 29 May 2019 08:59:25 +0000

̽��ֱ��Neptunian Desert is a region close to stars where large planets with their own atmospheres, similar to Neptune, are not expected to survive, since the strong irradiation from the star would cause any gaseous atmosphere to evaporate, leaving just a rocky core behind.

However, NGTS-4b, nicknamed the ‘Forbidden Planet’, still has its atmosphere intact and is the first exoplanet of its kind to be found in the Neptunian Desert. ̽��ֱ��results are reported in the Monthly Notices of the Royal Astronomical Society.

NGTS-4b is smaller than Neptune and three times the size of Earth. It is dense and hot, with a mass 20 times that of Earth and an average surface temperature of 1000 degrees Celsius. ̽��ֱ��planet orbits its star very closely, completing a full orbit in just 1.3 days.

̽��ֱ��planet was identified using the Next-Generation Transit Survey (NGTS) observing facility at the European Southern Observatory's Paranal Observatory in Chile’s Atacama Desert. NGTS is a collaboration between the Universities of Warwick, Leicester, Cambridge, and Queen’s ̽��ֱ�� Belfast, together with Observatoire de Genève, DLR Berlin and Universidad de Chile.

When looking for new planets, astronomers use facilities such as NGTS to look for a dip in the light of a star, which occurs when an orbiting planet passes in front of it, blocking some of the light. Usually, dips of 1% and more can be picked up by ground-based searches, but the NGTS telescopes can pick up a dip of just 0.2%.

This sensitivity means that astronomers can now detect a wider range of exoplanets: those with diameters between two and eight times that of Earth, in between the smaller rocky planets and gas giants.

“This is a very rare planet, and it’s the first time that such a small planet has been detected by a wide-field ground-based telescope,” said co-author Dr Ed Gillen from Cambridge’s Cavendish Laboratory, who led the data analysis of the system to determine the mass, radius and orbit of NGTS-4b.

̽��ֱ��researchers believe the planet may have moved into the Neptunian Desert recently, in the last one million years, or it was very big and the atmosphere is still evaporating.

“This planet must be tough - it is right in the zone where we expected Neptune-sized planets could not survive,” said lead Dr Richard West from the ̽��ֱ�� of Warwick. “It is truly remarkable that we found a transiting planet via a star dimming by less than 0.2% - this has never been done before by telescopes on the ground, and it was great to find after working on this project for a year.

“We are now searching our data for other similar planets to help us understand how dry this Neptunian Desert is, or whether it is greener than was once thought,” said Gillen.

̽��ֱ��research was supported in part by the UK Science and Technology Facilities Council.

Reference:
Richard G. West et al. ‘NGTS-4b: A sub-Neptune Transiting in the Desert.’ Monthly Notices of the Royal Astronomical Society (in press). DOI: 10.1093/mnras/stz1084

Adapted from a ̽��ֱ�� of Warwick press release.

An international group of astronomers has identified a rogue planet orbiting its star in the so-called Neptunian Desert.

This is a very rare planet, and it’s the first time that such a small planet has been detected by a wide-field ground-based telescope

Ed Gillen

̽��ֱ�� of Warwick/Mark Garlick

Artist's impression of NGTS-4b

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