While the transit method works best with space telescopes like Kepler for finding and studying new exoplanets, there are some special cases of where large exoplanets that orbit close to its star can be seen by ground based telescopes. Here is an interesting account of such an observation via the site Deep Sky Videos – Videos about the Depths of Space.
Category Archives: Astronomy
Video: “What’s Up – January 2016” – night sky highlights from JPL
A January night sky preview from NASA JPL:
NASA/ESA Hubble: The awakened force of a star
NASA/ESA Hubble Space Telescope study finds a feature in the cosmos that comes at the right time:
Perfectly timed for the release of “Star Wars Episode VII: The Force Awakens“, the NASA/ESA Hubble Space Telescope has imaged a cosmic double-bladed lightsabre. In the centre of the image, partially obscured by a dark Jedi-like cloak of dust, an adolescent star shoots twin jets out into space, demonstrating the fearsome forces of the Universe
This celestial lightsabre lies not in a galaxy far, far away, but within our home galaxy, the Milky Way. More precisely, it resides within a turbulent patch of space known as the Orion B molecular cloud complex, which is located just over 1350 light-years away in the constellation of Orion (The Hunter).
Bearing a striking resemblance to Darth Maul’s double-bladed lightsabre in Star Wars Episode One, the spectacular twin jets of material slicing across this incredible image are spewing out from a newly formed star that is obscured from view, cloaked by swirling dust and gas.
Zooming on HH 24: This video begins with a ground-based view of the night sky, before zooming on the knotted clumps of gas that make up the Herbig–Haro object 24, as the NASA/ESA Hubble Space Telescope sees it. Credit: ESA/Hubble, NASA, Digitized Sky Survey, N. Risinger (skysurvey.org). Music: Johan B Monell
When stars form within giant, gaseous clouds, some of the surrounding material collapses down to form a rotating, flattened disc encircling the nascent stars, which are known as protostars. This disc is where a potential planetary system might form. However, at this early stage, the star is mostly concerned with feeding its Jabba-like appetite. Gas from the disc rains down onto the protostar and, once nourished, the star awakens and jets of energised gas from its poles whirl out in opposite directions.
The Force is strong with these twin jets; their effect on their environment demonstrates the true power of the Dark Side with a blast stronger than one from a fully armed and operational Death Star battle station. As they stream away from one another at high speeds, supersonic shock fronts develop along the jets and heat the surrounding gas to thousands of degrees.
Furthermore, as the jets collide with the surrounding gas and dust and clear vast spaces, they create curved shock waves. These shockwaves are the hallmarks of Herbig-Haro (HH) objects — tangled, knotted clumps of nebulosity. The prominent Herbig-Haro object shown in this image is HH 24.
Just to the right of the cloaked star, a couple of bright points of light can be seen. These are young stars peeking through and showing off their own faint lightsabres. One hidden, cloaked source, only detectable in the radio part of the spectrum, has blasted a tunnel through the dark cloud in the upper left of the image with a wider outflow resembling “force lightning”.
Panning across HH 24: This video pans over NASA/ESA Hubble Space Telescope observations of the Herbig-Haro object 24. The two energetic jets as well as the dozens of knots of clumped gas are clearly visible. Credit: ESA/Hubble Music: Johan B Monell
All these jets make HH 24 the densest concentration of HH jets known in such a small region. Half of the HH jets have been spotted in this region in visible light, and about the same number in the infrared. Hubble’s observations for this image were performed in infrared light, which enabled the telescope to pierce through the gas and dust cocooning the newly-forming stars and capture a clear view of the HH objects that astronomers are looking for.
The stellar jets of HH 24 in 3D: This movie envisions a three-dimensional perspective on the Herbig-Haro object as it is seen by the NASA/ESA Hubble Space Telescope.
The sequence starts with a wide-field view covering the vast dark cloud of the Orion B molecular cloud complex and a scattering of stars. As the virtual camera flies into the dark nebula, the stars pass off-screen and the details of the forming stars and their red jets are revealed.
While the central star is hidden, its lightsabre-like jets peak out of the gas and dust. These jets have carved an hourglass-shaped cavity in the near side of the nebula.
The jet from another stellar newborn in this region has created a cylindrical tunnel through the gas extending to the left. Careful study of the Hubble data reveals a few other jets heating and displacing the gas and dust around them.
ESO: ALMA antennas find signs of new planets in discs around young stars
A new report from ESO (European Southern Observatory):
ALMA Reveals Planetary Construction Sites
New evidence for young planets in discs around young stars
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have found the clearest indications yet that planets with masses several times that of Jupiter have recently formed in the discs of gas and dust around four young stars. Measurements of the gas around the stars also provide additional clues about the properties of those planets.
Planets are found around nearly every star, but astronomers still do not fully understand how — and under what conditions — they form. To answer such questions, they study the rotating discs of gas and dust present around young stars from which planets are built. But these discs are small and far from Earth, and the power of ALMA was needed for them to reveal their secrets.
A special class of discs, called transitional discs, have a surprising absence of dust in their centres, in the region around the star. Two main ideas have been put forward to explain these mysterious gaps. Firstly, the strong stellar winds and intense radiation could have blown away or destroyed the encircling material [1]. Alternatively, massive young planets in the process of formation could have cleared the material as they orbit the star [2].
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have found telltale differences between the gaps in the gas and the dust in discs around four young stars. These new observations are the clearest indications yet that planets with masses several times that of Jupiter have recently formed in these discs. Credit: ALMA (ESO/NAOJ/NRAO)/M. Kornmesser
The unparalleled sensitivity and image sharpness of ALMA have now allowed the team of astronomers, led by Nienke van der Marel from the Leiden Observatory in the Netherlands to map the distribution of gas and dust in four of these transitional discs better than ever before [3]. This in turn has allowed them to choose between the two options as the cause of the gaps for the first time.
The new images show that there are significant amounts of gas within the dust gaps [4]. But to the team’s surprise, the gas also possessed a gap, up to three times smaller than that of the dust.
Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have found telltale differences between the gaps in the gas and the dust in discs around four young stars. These new observations are the clearest indications yet that planets with masses several times that of Jupiter have recently formed in these discs. Credit: ALMA (ESO/NAOJ/NRAO)/M. Kornmesser
This could only be explained by the scenario in which newly formed massive planets have cleared the gas as they travelled around their orbits, but trapped the dust particles further out [5].
“Previous observations already hinted at the presence of gas inside the dust gaps,” explains Nienke van der Marel. “But as ALMA can image the material in the entire disc in much greater detail than other facilities, we could rule out the alternative scenario. The deep gap points clearly to the presence of planets with several times the mass of Jupiter, creating these caverns as they sweep through the disc.”
Remarkably, these observations were conducted utilising just one tenth of the current resolving power of ALMA, as they were performed whilst half of the array was still under construction on the Chajnantor Plateau in northern Chile.
Further studies are now needed to determine whether more transitional discs also point towards this planet-clearing scenario, although ALMA’s observations have, in the meantime, provided astronomers with a valuable new insight into the complex process of planetary formation.
“All the transitional discs studied so far that have large dust cavities also have gas cavities. So, with ALMA, we can now find out where and when giant planets are being born in these discs, and compare these results with planet formation models,” says Ewine van Dishoeck, also of Leiden University and the Max Planck Institute for Extraterrestrial Physics in Garching [6]. “Direct planetary detection is just within reach of current instruments, and the next generation telescopes currently under construction, such as the European Extremely Large Telescope, will be able to go much further. ALMA is pointing out where they will need to look.”
Notes
[1] This process, which clears the dust and gas from the inside out, is known as photoevaporation.
[2] Such planets are difficult to observe directly (eso1310) and previous studies at millimetre wavelengths (eso1325) have failed to achieve a sharp view of their inner, planet-forming zones where these different explanations could be put to the test. Other studies (eso0827) could not measure the bulk of the gas in these discs.
[3] The four targets of these investigations were SR 21, HD 135344B (also known as SAO 206462), DoAr 44 and Oph IRS 48.
[4] The gas present in transitional discs consists primarily of hydrogen, and is traced through observations of the carbon monoxide — or CO — molecule.
[5] The process of dust trapping is explained in an earlier release (eso1325).
[6] Other examples include the HD 142527 (eso1301 and here) and J1604-2130 transitional discs.
ESA/Hubble: Study of 10 exo-Jupiter planets finds where the water is hiding
A report from the ESA/Hubble team:
Hubble reveals diversity of exoplanet atmospheres
Largest ever comparative study solves missing water mystery
Astronomers have used the NASA/ESA Hubble Space Telescope and the NASA Spitzer Space Telescope to study the atmospheres of ten hot, Jupiter-sized exoplanets in detail, the largest number of such planets ever studied. The team was able to discover why some of these worlds seem to have less water than expected — a long-standing mystery. The results are published in “Nature”.
Due to this difficulty, Hubble has only explored a handful of hot Jupiters in the past, across a limited wavelength range. These initial studies have found several planets to hold less water than expected (opo1436a, opo1354a).
This video shows an artist’s impression of the ten hot Jupiter exoplanets studied by David Sing and his colleagues. From top left to to lower left these planets are WASP-12b, WASP-6b, WASP-31b, WASP-39b, HD 189733b, HAT-P-12b, WASP-17b, WASP-19b, HAT-P-1b and HD 209458b…
Now, an international team of astronomers has tackled the problem by making the largest ever study of hot Jupiters, exploring and comparing ten such planets in a bid to understand their atmospheres [1]. Only three of these planetary atmospheres had previously been studied in detail; this new sample forms the largest ever spectroscopic catalogue of exoplanet atmospheres.
The team used multiple observations from both the NASA/ESA Hubble Space Telescope and NASA’s Spitzer Space Telescope. Using the power of both telescopes allowed the team to study the planets, which are of various masses, sizes, and temperatures, across an unprecedented range of wavelengths [2].
“I’m really excited to finally ‘see’ this wide group of planets together, as this is the first time we’ve had sufficient wavelength coverage to be able to compare multiple features from one planet to another,” says David Sing of the University of Exeter, UK, lead author of the new paper. “We found the planetary atmospheres to be much more diverse than we expected.”
All of the planets have a favourable orbit that brings them between their parent star and Earth. As the exoplanet passes in front of its host star, as seen from Earth, some of this starlight travels through the planet’s outer atmosphere. “The atmosphere leaves its unique fingerprint on the starlight, which we can study when the light reaches us,” explains co-author Hannah Wakeford, now at NASA Goddard Space Flight Center, USA.
These fingerprints allowed the team to extract the signatures from various elements and molecules — including water — and to distinguish between cloudy and cloud-free exoplanets, a property that could explain the missing water mystery.
The team’s models revealed that, while apparently cloud-free exoplanets showed strong signs of water, the atmospheres of those hot Jupiters with faint water signals also contained clouds and haze — both of which are known to hide water from view. Mystery solved!
“The alternative to this is that planets form in an environment deprived of water — but this would require us to completely rethink our current theories of how planets are born,” explained co-author Jonathan Fortney of the University of California, Santa Cruz, USA. “Our results have ruled out the dry scenario, and strongly suggest that it’s simply clouds hiding the water from prying eyes.”
The study of exoplanetary atmospheres is currently in its infancy, with only a handful of observations taken so far. Hubble’s successor, the James Webb Space Telescope, will open a new infrared window on the study of exoplanets and their atmospheres.
Notes
[1] To date, studies of exoplanet atmospheres have been dominated by a small number of well-studied planets. The team used Hubble and Spitzer observations of two such planets, HD 209458b (heic0303, opo0707b) and HD 189733b (heic1312, heic0720a), and used Hubble to observe eight other exoplanets — WASP-6b, WASP-12b, WASP-17b, WASP-19b, WASP-31b, WASP-39b, HAT-P-1b, HAT-P-12b. These planets have a broad range of physical parameters.
[2] The observations spanned from the ultraviolet (0.3 μm) to the mid-infrared (4.5 μm).