̽��ֱ�� of Cambridge - Hubble

Astronomers observe light bending around an isolated white dwarf

sc604 — Thu, 02 Feb 2023 08:08:58 +0000

Astronomers have directly measured the mass of a dead star using an effect known as gravitational microlensing, first predicted by Einstein in his General Theory of Relativity, and first observed by two Cambridge astronomers 100 years ago.

‘Sunscreen’ layer detected on distant planet

sc604 — Fri, 12 Jun 2015 09:17:29 +0000

̽��ֱ��presence of a stratosphere can provide clues about the composition of a planet and how it formed. This atmospheric layer includes molecules that absorb ultraviolet and visible light, acting as a kind of ‘sunscreen’ for the planet it surrounds. Until now, scientists were uncertain whether these molecules would be found in the atmospheres of large, extremely hot planets in other star systems.

̽��ֱ��results are published today (12 June) in ̽��ֱ��Astrophysical Journal.

“Detecting the presence of a stratosphere in an exoplanet and the chemical compound causing it is a major advancement in our ability to study exoplanetary atmospheres,” said co-author Dr Nikku Madhusudhan of the Institute of Astronomy at Cambridge.

In Earth’s atmosphere, the stratosphere sits above the troposphere – the turbulent, active-weather region that reaches from the ground to the altitude where nearly all clouds top out. In the troposphere, the temperature is warmer at the bottom – ground level – and cools down at higher altitudes.

̽��ֱ��stratosphere is just the opposite. In this layer, the temperature increases with altitude, a phenomenon called temperature inversion. On Earth, temperature inversion occurs because ozone in the stratosphere absorbs much of the sun’s ultraviolet radiation, preventing it from reaching the surface, protecting the biosphere, and therefore warming the stratosphere instead.

Similar temperature inversions occur in the stratospheres of other planets in our solar system, such as Jupiter and Saturn. In these cases, the culprit is a different group of molecules called hydrocarbons. Neither ozone nor hydrocarbons, however, could survive at the high temperatures of most known exoplanets, which are planets outside our solar system. This leads to a debate as to whether stratospheres would exist on them at all.

“Some of these planets are so hot in their upper atmospheres, they’re essentially boiling off into space,” said Avi Mandell, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a co-author of the study. “At these temperatures, we don’t necessarily expect to find an atmosphere that has molecules that can lead to these multi-layered structures.”

Using NASA’s Hubble Space Telescope, the researchers have settled this debate by identifying a temperature inversion in the atmosphere of WASP-33b, which has about four-and-a-half times the mass of Jupiter. Team members also think they know which molecule in WASP-33b’s atmosphere caused the inversion – titanium oxide.

“These two lines of evidence together make a very convincing case that we have detected a stratosphere on an exoplanet,” said Korey Haynes, lead author of the study. Haynes was a graduate student at George Mason ̽��ֱ�� in Fairfax, Virginia, and was working at Goddard with Mandell when the research was conducted.

̽��ֱ��researchers analysed observations made with Hubble’s Wide Field Camera 3 by co-author Drake Deming at the ̽��ֱ�� of Maryland. Wide Field Camera 3 can capture a spectrum of the near-infrared region where the signature for water appears. Scientists can use the spectrum to identify water and other gases in a distant planet’s atmosphere and determine its temperature.

Haynes and her colleagues used the Hubble observations, and data from previous studies, to measure emission from water and compare it to emission from gas deeper in the atmosphere. ̽��ֱ��team determined that emission from water was produced in the stratosphere at about 3300 degrees Celsius. ̽��ֱ��rest of the emission came from gas lower in the atmosphere that was at a temperature about 1650 degrees Celsius.

̽��ֱ��team also presented the first observational evidence that WASP-33b’s atmosphere contains titanium oxide, one of only a few compounds that is a strong absorber of visible and ultraviolet radiation and capable of remaining in gaseous form in an atmosphere as hot as this one.

“Understanding the links between stratospheres and chemical compositions is critical to studying atmospheric processes in exoplanets,” said Madhusudhan. “Our finding marks a key breakthrough in this direction.”

Inset image: NASA scientists detected a stratosphere and chemical compounds on WASP-33b by measuring light emitted from the dayside atmosphere of the planet observed as it passed behind its star (top). Temperatures in the stratosphere increase with height (right) because of molecules absorbing radiation from the star entering from the top and reemitting it locally; otherwise, temperatures would cool down at higher altitudes (left). Credit: NASA/GSFC

On a blazing-hot exoplanet known as WASP-33b, a team of astronomers including researchers from the ̽��ֱ�� of Cambridge has detected a stratosphere, one of the primary layers of Earth’s atmosphere.

Understanding the links between stratospheres and chemical compositions is critical to studying atmospheric processes in exoplanets

Nikku Madhusudhan

‘Sunscreen’ Layer on Extreme Planet

NASA/GSFC

On a massive planet around a nearby star, NASA’s Hubble Space Telescope has detected a stratosphere, one of the primary layers of the atmospheres of Earth and other planets in our solar system.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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Clear skies on exo-Neptune

sc604 — Wed, 24 Sep 2014 17:00:00 +0000

Astronomers have discovered clear skies and steamy water vapour on a gaseous planet outside our solar system. ̽��ֱ��planet, known as HAT-P-11b, is about the size of Neptune, making it the smallest-ever planet for which water vapour has been detected.

Using data from the NASA/ESA Hubble Space Telescope, the Spitzer Space Telescope, and the Kepler Space Telescope, an international team including astronomers from the ̽��ֱ�� of Cambridge found that HAT-P-11b is blanketed in water vapour, hydrogen gas, and other yet-to-be-identified molecules. ̽��ֱ��results are published today (24 September) in the online version of the journal Nature.

“This discovery is milepost on the road to eventually searching for molecules in the atmospheres of smaller, rocky planets more like Earth,” said John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate. “Such achievements are only possible when we combine the capabilities of these unique and powerful observatories.”

Clouds in the atmospheres of planets can block the view to underlying molecules that reveal information about the planets’ compositions and histories. Finding clear skies on a Neptune-size planet is a good sign that smaller planets might have similarly good visibility.

“When astronomers go observing at night with telescopes, they say ‘clear skies’ to mean good luck,” said Jonathan Fraine of the ̽��ֱ�� of Maryland, the study’s lead author. “In this case, we found clear skies on a distant planet. That's lucky for us because it means clouds didn't block our view of water molecules.”

HAT-P-11b is a so-called exo-Neptune — a Neptune-sized planet that orbits another star. It is located 120 light-years away in the constellation of Cygnus ( ̽��ֱ��Swan). Unlike Neptune, this planet orbits closer to its star, making one lap roughly every five days. It is a warm world thought to have a rocky core, a mantle of fluid and ice, and a thick gaseous atmosphere. Not much else was known about the composition of the planet, or other exo-Neptunes like it, until now.

Part of the challenge in analysing the atmospheres of planets like this is their size. Larger Jupiter-like planets are easier to observe and researchers have already been able to detect water vapour in the atmospheres of some of these giant planets. Smaller planets are more difficult to probe — and all the smaller ones observed to date have appeared to be cloudy.

̽��ֱ��team used Hubble’s Wide Field Camera 3 and a technique called transmission spectroscopy, in which a planet is observed as it crosses in front of its parent star. Starlight filters through the rim of the planet’s atmosphere and into a telescope. If molecules like water vapour are present, they absorb some of the starlight, leaving distinct signatures in the light that reaches our telescopes.

“We set out to look at the atmosphere of HAT-P-11b without knowing if its weather would be cloudy or not,” said Dr Nikku Madhusudhan, from Cambridge’s Institute of Astronomy, who was part of the study team. “By using transmission spectroscopy, we could use Hubble to detect water vapour in the planet. This told us that the planet didn’t have thick clouds blocking the view and is a very hopeful sign that we can find and analyse more cloudless, smaller, planets in the future. It is ground-breaking!”

Before the team could celebrate they had to be sure that the water vapour was from the planet and not from cool starspots — “freckles” on the face of stars — on the parent star. Luckily, Kepler had been observing the patch of sky in which HAT-P-11b happens to lie for years. Those visible-light data were combined with targeted infrared Spitzer observations. By comparing the datasets the astronomers could confirm that the starspots were too hot to contain any water vapour, and so it must belong to the planet.

̽��ֱ��results from all three telescopes demonstrate that HAT-P-11b is blanketed in water vapour, hydrogen gas, and other yet-to-be-identified molecules. So in fact it is not only the smallest planet to have water vapour found in its atmosphere but is also the smallest planet for which molecules of any kind have been directly detected using spectroscopy. Theorists will be drawing up new models to explain the planet’s makeup and origins.

Although HAT-P-11b is dubbed as an exo-Neptune it is actually quite unlike any planet in our Solar System. It is thought that exo-Neptunes may have diverse compositions that reflect their formation histories. New findings such as this can help astronomers to piece together a theory for the origin of these distant worlds.

“We are working our way down the line, from hot Jupiters to exo-Neptunes,” said Drake Deming, a co-author of the study also from ̽��ֱ�� of Maryland. “We want to expand our knowledge to a diverse range of exoplanets.”

̽��ֱ��astronomers plan to examine more exo-Neptunes in the future, and hope to apply the same method to smaller super-Earths — massive, rocky cousins to our home world with up to ten times the mass of Earth. Our solar system does not contain a super-Earth, but NASA’s Kepler mission is finding them around other stars in droves, and the NASA/ESA James Webb Space Telescope, scheduled to launch in 2018, will search super-Earths for signs of water vapour and other molecules. However, finding signs of oceans and potentially habitable worlds is likely a way off.

This work is important for future studies of super-Earths and even smaller planets. It could allow astronomers to pick out in advance the planets with atmospheres clear enough for molecules to be detected. Once again, astronomers will be crossing their fingers for clear skies.

Smallest exoplanet ever found to have water vapour

This is a very hopeful sign that we can find and analyse more cloudless, smaller, planets in the future

Nikku Madhusudhan

NASA/JPL-Caltech

A Neptune-size planet with a clear atmosphere is shown crossing in front of its star in this artist's depiction

̽��ֱ��text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

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‘Polluted’ stellar graveyard gives glimpse of our Solar System after Sun’s implosion

fpjl2 — Thu, 09 May 2013 12:21:10 +0000

By chemically sampling the atmospheres of two dead stars in the Hyades cluster 150 light years away, researchers at Cambridge and NASA/ESA’s Hubble Space Telescope have discovered the building blocks for Earth-sized planets formed around the stars while they lived.

̽��ֱ��study offers insight into what will happen in our solar system when our Sun burns out 5 billion years from now. It is published today in Monthly Notices of the Royal Astronomical Society.

̽��ֱ��dead stars - called white dwarfs - are the burned-out cores of Sun-like stars. ̽��ֱ��finding suggests that terrestrial planets formed around these white dwarfs when they were young stars.

Researchers found the white dwarfs’ atmospheres “polluted” with silicon - rocky material that makes up Earth and other terrestrial planets in our solar system.

This silicon pollution likely occurred when the dwarf’s gravity shredded asteroids that got sucked in to its pull, after asteroid belts were initially disrupted by the gravity of surviving Jupiter-sized planets - with debris settling into a ring around the dead stars similar to the rings of Saturn.

“When these stars were born, they built planets, and there’s a good chance they are retaining some of them,” said lead investigator Dr Jay Farihi of Cambridge’s Institute of Astronomy.

“ ̽��ֱ��rocks we are seeing are evidence for the Lego building blocks of planets. Both of these stars show asteroids being thrown around, which tells us that rocky planet assembly is common.”

Although the cluster is relatively young at 625 million years old, the dead stars provide clues as to what might happen when our Sun eventually burns out:

After exhausting its hydrogen fuel, the Sun will likely puff up to a red giant and destroy several terrestrial planets including Earth, losing mass as it ejects outer layers.

̽��ֱ��balance of gravitational power between the Sun and Jupiter would change, wreaking havoc on the asteroids in the belt located between Mars and Jupiter. Some of these asteroids could veer too close to the Sun’s gravity, breaking them into debris that could be pulled into a ring around our dead Sun - similar to the inferred rings around the Hyades white dwarfs.

To conduct the new analysis, researchers used Hubble’s powerful Cosmic Origins Spectrograph to divide the stars’ ultraviolet light into its constituent colours, providing information on the chemical elements in the atmosphere.

̽��ֱ��silicon-carbon ratio in the stars’ atmospheres rules out everything except for rock, according to researchers, who say they have chemical evidence that this material is “at least as rocky as the most primitive bodies” in our own solar system.

“ ̽��ֱ��one thing the white dwarf pollution technique gives us that we just won’t get with any other planet-detection technique is the chemistry of a planet,” Farihi said.

“Based on the silicon-to-carbon ratio in our study, for example, we can actually say that this material looks like the stuff in our back yard. If you put this stuff into the hand of any human being they would be able to tell you this is a rock, they wouldn’t need to be a scientist. It’s something familiar to all of us.”

̽��ֱ��debris most likely polluted the white dwarfs’ atmosphere when asteroids wandered too close to the stellar relics. “Basically, you need planets to throw the rocks around. It’s pretty hard to imagine another mechanism than gravity that causes material to rain down onto the star.”

Farihi suggested that asteroids less than 100 miles across were probably gravitationally torn apart by the white dwarfs. ̽��ֱ��pulverized material was pulled into a ring that could superficially resemble Saturn’s rings. ̽��ֱ��dusty material swirling in the rings eventually settled onto the stars.

̽��ֱ��researchers estimated the asteroid’s size by measuring the amount of dust consumed by the stars, about 10 million grams per second - equal to a small river. They then compared that measurement with those from previous observations.

̽��ֱ��team plan to analyse more white dwarfs using the same technique to identify not only the rocks’ composition but also their parent bodies. “We have been using our solar system as a kind of a map, but I don’t know what the universe does,” Farihi said. “ ̽��ֱ��universe might be doing something different. We really want to build up a picture of the different families rocks.

“ ̽��ֱ��beauty of this technique is that whatever the universe is doing, we’ll be able to measure it. Is there another recipe for life? ̽��ֱ��chemistry can tell us. Hopefully, with Hubble and the upcoming ground-based 30-meter telescopes, we’ll be able to tell a story.

“We can build a picture of hundreds of these things and tell how often it looks like Earth and how often it looks weird and strange. Who knows, maybe we’ll find stuff we haven’t thought of yet.”

For more information, please contact fred.lewsey@admin.cam.ac.uk

Research indicates the existence of Earth-like planets in dead solar system through latest chemical analysis techniques

Is there another recipe for life? ̽��ֱ��chemistry can tell us

Jay Farihi

'Polluted' stellar graveyard gives glimpse of our Solar System after Sun's implosion

NASA, ESA, STScI, and Z. Levay (STScI)

This illustration is an artist’s impression of the thin, rocky debris disc discovered around the two Hyades white dwarfs. Rocky asteroids are thought to be perturbed by planets within the system and diverted inwards towards the star, where they break up,

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