Gaia finds candidates for interstellar ‘Oumuamua’s home


BARCELONA, (ESA).-Using data from ESA’s Gaia stellar surveyor, astronomers have identified four stars that are possible places of origin of ‘Oumuamua, an interstellar object spotted during a brief visit to our Solar System in 2017. 

The discovery last year sparked a large observational campaign: originally identified as the first known interstellar asteroid, the small body was later revealed to be a comet, as further observations showed it was not slowing down as fast as it should have under gravity alone.

The most likely explanation of the tiny variations recorded in its trajectory was that they are caused by gasses emanating from its surface, making it more akin to a comet.

But where in the Milky Way did this cosmic traveller come from?  

Comets are leftovers of the formation of planetary systems, and it is possible that ‘Oumuamua was ejected from its home star’s realm while planets were still taking shape there. To look for its home, astronomers had to trace back in time not only the trajectory of the interstellar comet, but also of a selection of stars that might have crossed paths with this object in the past few million years.  

“Gaia is a powerful time machine for these types of studies, as it provides not only star positions but also their motions,” explains Timo Prusti, Gaia project scientist at ESA. 
To this aim, a team of astronomers led by Coryn Bailer-Jones at the Max Planck Institute for Astronomy in Heidelberg, Germany, dived into the data from Gaia’s second release, which was made public in April. 

The Gaia data contain positions, distance indicators and motions on the sky for more than a billion stars in our Galaxy; most importantly, the data set includes radial velocities – how fast they are moving towards or away from us – for a subset of seven million, enabling a full reconstruction of their trajectories. The team looked at these seven million stars, complemented with an extra 220 000 for which radial velocities are available from the astronomical literature. 

As a result, Coryn and colleagues identified four stars whose orbits had come within a couple of light years of ‘Oumuamua in the near past, and with relative velocities low enough to be compatible with likely ejection mechanisms.  

All four are dwarf stars – with masses similar to or smaller than our Sun’s – and had their ‘close’ encounter with the interstellar comet between one and seven million years ago. However, none of them is known to either harbour planets or to be part of a binary stellar system; a giant planet or companion star would be the preferred mechanism to have ejected the small body. 

While future observations of these four stars might shed new light on their properties and potential to be the home system of ‘Oumuamua, the astronomers are also looking forward to future releases of Gaia data. At least two are planned in the 2020s, which will include a much larger sample of radial velocities, enabling them to reconstruct and investigate the trajectories of many more stars. 

“While it’s still early to pinpoint ‘Oumuamua’s home star, this result illustrates the power of Gaia to delve into the history of our Milky Way galaxy,” concludes Timo.

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Tags: MILKY WAY Gaia Oumuamua Comet Asteroid

Sea-level rise


BARCELONA, (ESA).-Although it may not be immediately obvious when we visit the beach, sea-level rise is affecting coastlines all over the world. 

For low-lying countries such as the Netherlands, sea-level rise and tidal surges are a constant threat. Our oceans are rising as a consequence of climate change. 

As the temperature of seawater increases it expands and the ice melting from ice sheets and glaciers adds more water to the global ocean. We know this because satellites high above our heads measure the temperature of the sea surface and of our changing ice.

While the global averaged trend is towards rising levels, there are many regional differences so that in some places it is rising and in other places it is falling. 

Satellites carrying altimeter instruments systematically measure the height of the sea surface so that sea-level rise can be closely monitored. 

Altimetry measurements over the last 25 years show that on average sea-level is rising about 3 mm a year and this rise is accelerating.

Copyright: ESA

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Tags: ESA Sea-level Netherlands Climate change

Dust stoms on Titan spotted by Cassini for the first time


BARCELONA, (ESA).-Data from the international Cassini spacecraft that explored Saturn and its moons between 2004 and 2017 has revealed what appear to be giant dust storms in equatorial regions of Titan. 

The discovery, described in a paper published in Nature Geoscience today, makes Titan the third body in the Solar System where dust storms have been observed – the other two are Earth and Mars.   

The observation is helping scientists to better understand the fascinating and dynamic environment of Saturn’s largest moon. 

“Titan is a very active moon,” says Sebastien Rodriguez, an astronomer at the University Paris Diderot, France, and the lead author of the paper.  

“We already know that about its geology and exotic hydrocarbon cycle. Now we can add another analogy with Earth and Mars: the active dust cycle.” 

Complex organic molecules, which result from the atmospheric chemistry and, once large enough, eventually fall to the surface, can be raised from large dune fields around Titan’s equator. 

Titan is an intriguing world – in a way quite similar to Earth. In fact, it is the only moon of the Solar System with a substantial atmosphere and the only celestial body other than our planet where stable bodies of surface liquid are known to still exist.  

There is one big difference though: while on Earth such rivers, lakes and seas are filled with water, on Titan it is primarily methane and ethane that flows through these liquid reservoirs. In this unique methane cycle, the hydrocarbon molecules evaporate, condense into clouds and rain back onto the ground.  

The weather on Titan varies from season to season, just as it does on Earth. In particular around the equinox, the time when the Sun crosses Titan’s equator, massive clouds can form in tropical regions and cause powerful methane storms. Cassini observed such storms during several of its Titan flybys.  

When Sébastien and his team first spotted three unusual equatorial brightenings in infrared images taken by Cassini around the moon’s 2009 northern equinox, they thought these might be exactly such methane clouds. A thorough investigation revealed they were something completely different, however. 

“From what we know about cloud formation on Titan, we can say that such methane clouds in this area and in this time of the year are not physically possible,” says Sébastien. 

“The convective methane clouds that can develop in this area and during this period of time would contain huge droplets and must be at a very high altitude, much higher than the 10 km that modelling tells us the new features are located.”
The researchers were also able to rule out that the features were actually on the surface in the form of frozen methane rain or icy lavas. Such surface spots would have a different chemical signature and remain visible for much longer, while the bright features in this study were only visible for 11 hours to five weeks. 

Modelling also showed that the features must be atmospheric, but still close to the surface – most likely forming a very thin layer of tiny solid organic particles. Since they were located right over the dune fields around Titan’s equator, the only remaining explanation was that the spots were actually clouds of dust raised from the dunes.
Sébastien says that while this is the first ever observation of a dust storm on Titan, the finding is not surprising. 

“We believe that the Huygens probe, which landed on the surface of Titan in January 2005, raised a small amount of organic dust upon arrival due to its powerful aerodynamic wake,” says Sébastien. 

“But what we spotted here with Cassini is at a much larger scale. The near-surface wind speeds required to raise such an amount of dust as we see in these dust storms would have to be very strong – about five times as strong as the average wind speeds estimated by the Huygens measurements near the surface and with climate models.”

Huygens made only one direct measurement of the speed of the surface wind just before its landing on Titan, and at that time it was very low, less than 1 metre per second.  

“For the moment, the only satisfactory explanation for these strong surface winds is that they might be related to the powerful gusts that may arise in front of the huge methane storms we observe in that area and season,” concludes Sébastien.  

This phenomenon, called ‘haboob’, can also be observed on Earth with giant dust clouds preceding storms in arid areas. 

The existence of such strong winds generating massive dust storms also implies that the underlying sand can be set in motion, too, and that the giant dunes covering Titan’s equatorial regions are still active and continually changing.   

The winds could be transporting the dust raised from the dunes across large distances, contributing to the global cycle of organic dust on Titan, and causing similar effects to those that can be observed on Earth and Mars.

Copyright: IPGP/Labex UnivEarthS/University Paris Diderot – C. Epitalon & S. Rodriguez

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Tags: Mars ESA Cassini Titan Earth Dust storms Saturn

Shedding light on shallow waters


BARCELONA, (ESA).-Keeping an eye on our waters is more important than ever, as widespread drought continues to sweep Europe this summer. 

Earth’s changing sea levels are crucial indicators of how our environment is fairing, but monitoring it manually can be a labour-intensive, expensive, and at times even dangerous task. 

Coastal areas provide additional complications, as shifting seabeds and currents make creating accurate and consistent water depth maps – also known as bathymetry – almost impossible. 

Satellites are ideally placed to address this challenge, however.
Low-orbiting satellites equipped with light-measuring sensors can record how much light is reflected off the seabed, gathering and updating the information continually as they fly over. 

An ESA-backed group, led by TCarta, has developed a way of using this data to produce water depth maps, and make them available to anyone who could use them. 

Richard Flemmings, Operations Director for TCarta, said: “The team applies computer algorithms to satellite imagery from sources like Landsat, Sentinel-2 and DigitalGlobe’s WorldView constellation. 

“These algorithms analyse the images’ light frequency from different parts of the satellite’s spectral range, and work with existing points of reference, such as confirmed results drawn from similar readings elsewhere, and knowledge on how different types of seabed reflect the light. 

“These products are hosted on the Bathymetrics Data Portal, which provides ready-made, instantly available and high resolution bathymetry at a fraction of the cost of traditional methods.” 

Different satellites can generate different resolution images, with Copernicus’s Sentinel-2 wide swath high-resolution multispectral imager producing around 10m, for example, although the portal also hosts resolutions of up to 2m. 

Detailed information on water levels that can be obtained immediately is extremely valuable for environmental agencies, but also has other uses.
Industries that conduct their business in or through the water require this kind of data to do so in the safest and most cost-effective manner. 

Energy infrastructure development, for example, requires up-to-date information on water depths over large areas to identify the best routes to lay pipes, while port construction needs reliable and long-term data for a concentrated location, in order to plan when and how the structure should be built. 

The Bathymetrics Data Portal was launched with help from ESA’s Business Applications programme, which co-funded an earlier, demonstration version.
ESA’s Business Applications programme is the mark of Europe’s best commercial ventures powered by Space. It is the commercial arm of the European Space Agency and aims to prove that space is open for business with the power to improve everyday life. 

Since the programme’s inception in 2008, ESA Business Applications has invested more than €200M in over 500 business ideas addressing markets in industries worldwide, like the Bathymetrics Data Portal. 

Typical funding ranges from €60k to €2M and is used from early stage feasibility studies to large-scale demonstration projects.

Copyright: ESA / TCarta

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Tags: ESA Europe Richard Flemmings TCarta

Herschel’s view of the Galactic Centre


BARCELONA, (ESA).-An odd-shaped formation of gas and dust at the centre of the Milky Way, captured by the far-infrared cameras on board ESA’s Herschel space observatory. The nearly continuous strip of dense and cold clumps of material forms an infinity symbol, or sideways 8, that is a few hundred light years across. In this image, the strip twists around an invisible axis running roughly from the top left to the bottom right.

The infinity-shaped loop, estimated to have a whopping 30 million solar masses, is made up of dense gas and dust at a temperature of just 15 degrees above absolute zero. Displayed in yellow in the image, it contrasts with warmer, less dense gas and dust from the centre of the Galaxy that appears inside the strip and is coloured in blue. Surrounding the loop is cool gas, painted in red-brownish tones.

The ring and its surroundings harbour a number of star-forming regions and young stars, which stand out in bright-blue colour in the image. The area is part of the Central Molecular Zone, a region at the centre of the Milky Way permeated with molecular clouds, which are ideal sites for star formation.

The Galactic Centre is located almost 30,000 light years away from the Sun, in the direction of the Sagittarius constellation. It is a complex and dynamic place, with emission nebulae and supernova remnants – in addition to star-forming molecular clouds – surrounding the supermassive black hole that sits at our Galaxy’s core. The gas and dust in this region appears mostly dark when viewed through an optical telescope, but it can be seen clearly with Herschel’s instruments.

This image was captured by the Herschel’s PACS (Photodetector Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging REceiver) far-infrared cameras, and it was first published in 2011. Obtained as part of Hi-GAL, the Herschel infrared Galactic Plane Survey, it combines observations at three different wavelengths: 70 microns (blue), 160 microns (green) and 250 microns (red).

Herschel was an ESA space observatory active from 2009 to 2013. At the time of its launch, it had the largest telescope ever sent into space.

Copyright: ESA / NASA / JPL-Caltech / Hi-GAL

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Tags: ESA MILKY WAY Herschel Space Observatory