An artist's conception of two magnetic fields interacting in a bow shock. Image credit: NASA
Astronomers may soon be able to observe the shockwaves between the magnetic fields of exoplanets and the flow of particles from the stars they orbit.
Magnetic fields are crucial to a planet’s (and as it turns out a moon’s) habitability. They act as protective bubbles, preventing harmful space radiation from stripping away the object’s atmosphere entirely and even reaching the surface.
An extended magnetic field – known as a planetary magnetosphere – is created by the shock between the stellar wind and the intrinsic magnetic field of the planet. It has the potential to be huge. Within our own Solar System, Jupiter’s magnetosphere extends to distances up to 50 times the size of the planet itself, nearly reaching Saturn’s orbit.
When the wind of high-energy particles from the star hits the planetary magnetosphere, it interacts in a bow shock that diverts the wind and compresses the magnetosphere.
Recently a team of astronomers, led by PhD student Joe Llama of the University of St. Andrews, Scotland, have worked out how we might observe planetary magnetospheres and stellar winds via their bow shocks.
Llama took a careful look at the planet HD 189733b, located 63 light years away toward the constellation Vulpecula. From the Earth, the planet is seen to transit its host star every 2.2 days, causing a dip in the overall light from the system.
As a bright star, HD 189733b has been studied extensively by astronomers. Data collected in July 2008 by the Canada-France-Hawaii telescope mapped the star’s magnetic field. While the magnetic field varied, it was on average 30 times greater than that of our Sun – meaning that the stellar wind is much higher than the solar wind.
This allowed the team to carry out extensive simulations of the stellar wind around HD 189733b – characterizing the bow shock created as the planet’s magnetosphere passes through the stellar wind. With this information they were able to simulate the light curves that would result from the planet and the bow shock orbiting the star.
The bow shock leads the planet – causing the light to drop a little earlier than expected. The amount of light blocked by the bow shock, however, will change as the planet moves through a variable stellar wind. If the stellar wind is particularly strong, the resulting bow shock will be strong, and the transit depth will be greater. If the stellar wind is weak, the resulting bow shock will be weak, and the transit depth will be less.
The video below shows the light curve of a bow shock and exoplanet.
“We found that the shockwave between the stellar and planetary magnetic fields will change drastically as activity on the star varies,” Llama told Universe Today. “As the planet passes through very dense regions of the stellar wind, so the shock will become denser, the material in it will block more light and therefore cause a larger dip in the transit making it more detectable.”
While there were no transit observations for this study, this theoretical outlook demonstrates that it will be possible to detect the bow shock, and therefore the magnetic field, of a distant exoplanet. Dr. Llama comments: “This will help us to better identify potentially habitable worlds.”
The paper has been accepted for publication in Monthly Notices of The Royal Astronomical Society and is available for download here.
A global view of Mercury, as seen by MESSENGER. Credit: NASA
Three to two. That’s the ratio of the time it takes Mercury to go around the sun (88 days) in relation to its rotation (58 days). This is likely due to the influence of the Sun’s immense gravity on the planet. A new study confirms that finding, while stating something even more interesting: other star systems could see the same type of resonance.
Hundreds of confirmed exoplanets have been found so far, many of them in very tight configurations, the authors said. “Mercury-like states should be common among the hundreds of discovered and confirmed exoplanets, including potentially habitable super-Earths orbiting M-dwarf [red dwarf] stars,” they added. “The results of this investigation provide additional insight into the possibilities of known exoplanets to support extraterrestrial life.”
Habitability, of course, depends on many metrics. What kind of star is in the system, and how stable is it? How far away are the planets from the star? What is the atmosphere of the planet like? And as this study points out, what about if one side of the planet is tidally locked to its star and spends most or all of its time with one side facing the starshine?
Additionally, the study came up with an explanation as to why Mercury remains in a 3:2 orbit in opposition to, say, the Moon, which always has one side facing the Earth. The study took into account factors such as internal friction and a tidal “bulge” that makes Mercury appear slightly misshapen (and which could slow it down even further.) Basically, it has to do with Mercury’s early history.
From Orbit, Looking toward Mercury’s Horizon. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
“Among the implications of the released study are, to name a few, a fast tidal spin-down, a relatively cold (i.e., not fully molten) state of the planet at the early stages of its life, and a possibility that the internal segregation and formation of the massive liquid core happened after Mercury’s capture into the resonance,” the press release added.
The results were presented today (Oct. 7) at the American Astronomical Society department of planetary sciences meeting held in Denver. A press release did not make clear if the study has been submitted for peer review or published.
Is it Friday already? Then it’s time for another Weekly Space Hangout. Join a team of dedicated space journalists to discuss the big space and astronomy news stories that broke this week. This time around, we discussed Amy Shira Teitel’s Buran article, ISON Watch 2013, and the re-re-discovery of water on Mars.
We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern, 2000 GMT. You can watch from here on Universe Today, or over on Google+ or YouTube.
An artist's conception of a disintegrating planet - creating a trail of dust - around its rocky star.
Solar flares – huge eruptions of charged particles from the Sun – present little threat to Earth. On a few rare occasions these particles may disrupt our communications systems and cause radio blackouts. But they tend to be more aesthetically pleasing than harmful. It’s certainly a sight to be seen as these energetic particles collide with our atmosphere, resulting in a cascade of colorful lights – the aurora borealis.
Fortunately our planet provides the protection necessary from such harmful space radiation. But not all planets are quite so lucky. Take for instance Kepler’s latest object of interest: KIC 12557548b, a super Mercury-size planet candidate. Astronomers have recently found that due to this star’s activity – producing massive stellar flares – the planet itself is evaporating.
Only last year, four different sources published evidence that this rocky planet was disintegrating. Thanks to Kepler, it quickly became clear that the total amount of light from KIC 12557548 as a function of time – the light curve of the system – dropped every 15.7 hours as a planet orbited it. But the amount of light blocked due to the transiting planet varied from 0.2% to more than 1.2%.
The amount of light blocked is dependent on the size of the planet. A Jupiter-size planet will block more light than a Mercury-size planet. The variations here suggest a range for the size of the planet: from a super Mercury-sized planet to a Jupiter-sized planet.
But this wasn’t the planet’s only enigma. It also has an asymmetric light curve. The total light from the star drops steadily as the planet begins its transit, plateaus as the planet fully covers the disk of the star, and then increases as the planet ends its transit. But the rate at which the light drops is much faster than the rate at which it increases. It takes longer for the light curve to return to its original brightness, hinting at a tail of debris that trails the planet, continuing to block light.
The light curves of KIC 12557548b. The left-hand plot represents deep transits, whereas the right-hand plot represents more shallow transits. Both plots show a clear asymmetry. Source: Brogi et al. 2012
It appears that the planet is evaporating – emitting small particles of dust into orbit, which then trails behind it. The varying transit depth reflects the amount of dust currently evaporating.
Recently a team from the University of Tokyo analyzed the system in more detail, attempting to explain why this tiny planet is evaporating. “We found that the transit depth negatively correlates with the modulation of the stellar flux,” Dr. Kawahara, lead author on the study, told Universe Today. “The dust amount increases when the planet is located in front of the star spots.”
The transit depth does not vary randomly, but every 22.83 days. This coincides with the modulation of the stellar flux, or simply the stellar rotation period. Star spots may be indirectly detected by a star’s noticeable decrease in stellar flux. Because these star spots are large (much larger than sunspots) they last for long periods of time, and may be used to deduce the star’s rotation period.
Kawahara et al. found that the transit depth periodically varies with the stellar rotation rate – finding a correlation between stellar activity and the rate at which the planet is evaporating.
“Energy from the star spots increases the amount of dust and atmosphere from the planet,” explains Dr. Kawahara. The extreme heat and wind is enough to speed up the motions of the dust molecules; making them fast enough to escape the planet’s gravitational pull.
Future spectroscopic studies may search for molecules in the evaporating atmosphere of KIC 12557548b. But Dr. Kawahara remarks that due to the planet’s faintness it is unlikely. His best hope is that future studies may instead find a similar object closer to us, that may be more easy to study.
The finding is published in The Astrophysical Journal Letters and is available for download here.
We missed a week, but now we’re back with the Weekly Space Hangout… back with a vengeance, with a full crew of 8 space journalists. We talked about the upcoming LADEE Launch, the test flight of SpaceShipTwo, an interview with Chris Kraft and much much more.
We broadcast the Weekly Space Hangout as a live Google+ Hangout on Air every Friday at 12:00pm Pacific / 3:00pm Eastern. You can watch the show on Universe Today, or from the Cosmoquest Event when we post it.
The life-cycle of a Sun-like star from protostar (left side) to red giant (near the right side) to white dwarf (far right). Credit: ESO/M. Kornmesser
If you want a picture of how you’ll look in 30 years, youngsters are told, look at your parents. The same principle is true of astronomy, where scientists compare similar stars in different age groups to see how they progress.
We have a special interest in learning how the Sun will look in a few billion years because, you know, it’s the main source of energy and life on Earth. Newly discovered HIP 102152 could give us some clues. The star is four billion years older than the sun, but so close in composition that researchers consider it almost like a twin.
Telescopes have only been around for a few centuries, making it hard to project what happens during the billions upon billions of years for a star’s lifetime. We have about 400 years of observations on the sun, for example, which is a minute fraction of its 4.6 billion-year-old lifespan so far.
Today, we take telescopic observations of the Sun for granted, but the technology only became available about 400 years ago. This picture shows the Sun in H-Alpha, on 01-07-2013, using a Lunt Solar LS60Scope/LS50 Hydrogen Alpha Solar filter. Credit: John Chumack
“It is very hard to study the history and future evolution of our star, but we can do this by hunting for rare stars that are almost exactly like our own, but at different stages of their lives,” stated the European Southern Observatory.
ESO’s Very Large Telescope — guided by a team led by the University of Sao Paulo’s Jorge Melendez — examined HIP 102152 with a spectrograph that broke up the light into various colors, revealing properties such as chemical composition. Around the same time, they scrutinized 18 Scorpii, also considered to be a twin but one that is younger than the sun (2.9 billion years old)
So what can we predict about the Sun’s future? One thing puzzling scientists has been the amount of lithium in our closest stellar companion. Although the Big Bang (the beginning of the universe) created hydrogen, helium and lithium, only the first two elements are abundant in the Sun.
Periodic Table of Elements
HIP 102152, it turns out, also has low levels of lithium. Why isn’t clear yet, ESO notes, although “several processes have been proposed to transport lithium from the surface of a star into its deeper layers, where it is then destroyed.” Previous observations of young Sun-like stars also show higher levels of lithium, implying something changes between youth and middle age.
The elder twin to our Sun may host another discovery: there could be Earth-sized planets circling the star. Chemical properties of HIP 102152 show that it has few elements that you see in meteorites and rocky planets, implying the elements are “locked up” in bodies close to the star. “This is a strong hint that HIP 102152 may host terrestrial rocky planets,” ESO stated.
Better yet, separate observations showed that there are no giant planets close to the star — leaving room for Earth-sized planets to flourish.
It’s time for the Weekly Space Hangout. This is our weekly rundown on all the big space news stories of the week, explained by a dedicated team of space journalists.
Host:Fraser Cain
Panel: Alan Boyle, Brian Koberlein, Jason Major, Nicole Gugliucci
We broadcast the Weekly Space Hangout every Friday afternoon as a live Google+ Hangout. You can join us live on Google+, YouTube or right here on Universe Today every Friday at 12:00 pm Pacific / 3:00 pm Eastern.
Astronomers have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets. The graph shows the spectrum of one of the globulettes taken at the 20-metre telescope at Onsala Space Observatory. Radio waves from molecules of carbon monoxide (13CO) give information on the mass and structure of these clouds. ESO/M. Mäkelä.
Free-floating rogue planets are intriguing objects. These planet-sized bodies adrift in interstellar space were predicted to exist in 1998, and since 2011 several orphan worlds have finally been detected. The leading theory on how these nomadic planets came to exist is that they were they ejected from their parent star system. But new research shows that there are places in interstellar space that might have the right conditions to form planets — with no parent star required.
Artistic representations of the only known planets around other stars (exoplanets) with any possibility to support life as we know it. Credit: Planetary Habitability Laboratory, University of Puerto Rico, Arecibo.
The International Astronomical Union issued a statement on August 14, 2013 that they have changed their official stance on two things: 1. assigning popular names to the numerous extrasolar planets being discovered, and 2. allowing the public to be involved in that naming process.
“It is therefore in line with a long-established global tradition and experience that the IAU fully supports the involvement of the general public, whether directly or through an independent organised vote, in the naming of planetary satellites, newly discovered planets and their host stars,” the online statement said.
This new stance came as a surprise to many.
“I was surprised by the IAU statement encouraging the general public input on naming astronomical objects,” said Professor Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico, in an email to Universe Today. “This is certainly something good. …So there is now a public naming procedure that includes the IAU validation but this does not exclude any other non-IAU public naming campaigns.”
As recently as late March, 2013, the IAU’s official word on naming exoplanets was, “the IAU sees no need and has no plan to assign names to these objects at the present stage of our knowledge.”
Their rationale was since there is seemingly going to be so many exoplanets, it will be difficult to name them all.
“…the IAU greatly appreciates and wishes to acknowledge the increasing interest from the general public in being more closely involved in the discovery and understanding of our Universe. As a result in 2013 the IAU Commission 53 Extrasolar Planets and other IAU members will be consulted on the topic of having popular names for exoplanets, and the results will be made public on the IAU website.”
Artistic rendition of a sunset view from the perspective of an imagined Earth-like moon orbiting the giant planet, PH2 b. Image Credit: H. Giguere, M. Giguere/Yale University
This new decision follows a line of events earlier this year where the SETI Institute and the space company Uwingu organized their own campaigns/contests for creating popular names of objects in space instead of the rather clinical, scientific names currently assigned to planets, such as HD 41004 Ab. Both events were wildly popular with the general public, but generated discussion about how “official” the names would be. The IAU issued a statement regarding the contests saying that while they welcomed the public’s interest in being involved in recent discoveries, as far as they are concerned, the IAU has the last word. Additionally, they were against “selling” names (Uwingu charged a fee to suggest a name and to vote as a fundraiser for space research.)
“In the light of recent events, where the possibility of buying the rights to name exoplanets has been advertised, the International Astronomical Union (IAU) wishes to inform the public that such schemes have no bearing on the official naming process. The IAU… would like to strongly stress the importance of having a unified naming procedure,” said the April 12, 2013 statement issued by the IAU.
Public naming campaigns are also “sanctioned” given they follow a set of rules:
1. Prior to any public naming initiative, often a vote (hereafter “the process”), the IAU should be contacted from the start by Letter of Intent sent to the IAU General Secretary;
2. The process should be submitted in the form of a proposal to the IAU by an organization. Scientists or science communicators may be involved in the process;
3. The organization should list its legal or official representatives and its goals, and explain the reasons for initiating the process for naming a particular object or set of objects;
4. The process cannot request nor make reference to any revenues, for whatever purpose;
5. The process must guarantee a wide international participation;
6. The public names proposed (whether by individuals or in a naming campaign)should follow the naming rules and restrictions adopted for Minor Bodies of the Solar System, by the IAU and by the Minor Planet Center (see here and here
for more details.
Among other rules are that proposed names should be 16 characters or less in length, pronounceable in as many languages as possible, non-offensive in any language or culture, and that names of individuals, places or events principally known for political or military activities are unsuitable.
Also, the names must have the formal agreement of the discoverers.
The new statement also has its critics. People joked on Twitter this morning whether the name of our neighboring planet Mars, named for the god of war, will have to be changed due to the new restrictions on military nomenclature.
Astronomer Alan Stern, principal investigator of the New Horizons mission to Pluto and CEO of Uwingu said he was actually not surprised at the IAU’s new statement.
“Fundamentally it’s still about the public being subservient to IAU committees that pass on recommendations,” he said via an email response to Universe Today. “Old school. Why should the IAU be a traffic cop?”
Stern also said the new statement has several contradictions from the statement the IUA put out on April 12 of this year, such as that “these [naming]campaigns have no bearing on the official naming process — they will not lead to an officially-recognised exoplanet name, despite the price paid or the number of votes accrued.” It now would appear that contests that follow the IAU’s rules are OK.
Stern said he has received letters and emails of support from other astronomers, particularly on the “no revenue” provision, noting how astronomy publications and planetariums charge money for their magazines and sky shows.
“If they can do it, why can’t Uwingu — especially since Uwingu’s revenue is used (at least in part) to further the IAU’s own goals, namely, to advance the science of astronomy, and the public’s understanding of it, worldwide?,” Stern quoted one email he received.
Also, the April statement from the IAU said they were the single arbiter of the naming process of celestial objects, while the new August statement says, “The IAU does not consider itself as having a monopoly on the naming of celestial objects— anyone can in theory adopt names the way they choose.”
The statement goes on, “However, given the publicity and emotional investment associated with these discoveries, worldwide recognition is important and the IAU offers its unique experience for the benefit of a successful public naming process (which must remain distinct, as in the past, from the scientific designation issues).”
Since this is a public debate about the public’s involvement in providing popular names for astronomical objects, please add your thoughts in the comments.
This graphic depicts HD 189733b, the first exoplanet caught passing in front of its parent star in X-rays. Credit: X-ray: NASA/CXC/SAO/K.Poppenhaeger et al; Illustration: NASA/CXC/M.Weiss.
In the medical field, X-rays are used for finding and diagnosing all sorts of ailments hidden inside the body; in astronomy X-rays can also be used to study obscured objects like pulsars and black holes. Now, for the first time, X-rays have been used to study another object in space that tends to be difficult to spot: an extra solar planet. The Chandra X-ray Observatory and the XMM Newton Observatory combined their X-ray super powers to look at an exoplanet passing in front of its parent star.
This is not a new detection of an exoplanet – this same exoplanet, named HD 189733b has been one of the most-observed planets orbiting another star, and was recently in the news for Hubble confirming the planet’s ocean-blue atmosphere and the likelihood of having glass raining down on the planet.
But being able to see the exoplanet in X-rays is good news for future studies and perhaps even detections of planets around other stars.
“Thousands of planet candidates have been seen to transit in only optical light,” said Katja Poppenhaeger of Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., who led the new study, which will be published in the Aug. 10 edition of The Astrophysical Journal. “Finally being able to study one in X-rays is important because it reveals new information about the properties of an exoplanet.”
Artist’s impression of the deep blue planet HD 189733b, based on observations from the Hubble Space Telescope. Credit: NASA/ESA.
HD 189733b is a Jupiter-sized extrasolar planet orbiting a yellow dwarf star that is in a binary system called HD 189733 in the constellation of Vulpecula, near the Dumbell Nebula, approximately 62 light years from Earth.
This huge gas giant orbits very close to its host star and gets blasted with X-rays from its star — tens of thousands of times stronger than the Earth receives from the Sun — and endures wild temperature swings, reaching scorching temperatures of over 1,000 degrees Celsius. Astronomers say it likely rains glass (silicates) – sideways — in howling 7,000 kilometer-per-hour winds.
But it is relatively close to Earth, and so it has been oft-studied by many other space and ground-based telescopes.
In a blog post, Poppenhaeger said she was inspired by the launch of the Kepler telescope, and wondered if exoplanets could be seen in X-rays. She was excited when she found archived data from XMM Newton showing a fifteen hour long observation of the star HD 189733 and the “Hot Jupiter” HD 189733b was crossing in front of the star during that observation.
But the light curve was disappointing, she said. “The star is magnetically active, meaning that its corona is bright and flickering, so its X-ray light curve showed lots of scatter. Looking for a transit signal in this light curve was like trying to hear a whisper in a noisy pub,” Poppenhaeger wrote.
She knew with more data, the transit signal would be clearer, so she applied for – and got – time on Chandra to observe this exoplanet.
She combined the data from all the observations and was finally successful. “I could detect the transit of the planet in X-rays,” Poppenhaeger said. “What surprised me was how deep the transit was: The planet swallowed about 6-8% of the X-ray light from the star, while it only blocked 2.4% of the starlight at optical wavelengths. That means that the planet’s atmosphere blocks X-rays at altitudes of more than 60,000 km above its optical radius – a 75% larger radius in X-rays!”
That means that the outer atmosphere has to be heated up to about 20,000 K to sustain itself at such high altitudes. Additionally, the planet loses its atmosphere about 40% faster than thought before.
Poppenhaeger said she and her colleagues will test more X-ray observations of other similar planets such as CoRoT-2b to learn more about how stars can affect a planet’s atmosphere.
