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Showing posts with label Space & Astrophysics. Show all posts
Showing posts with label Space & Astrophysics. Show all posts

Tuesday, 19 November 2019

NASA confirms the presence of water vapor on the surface of Europa

The fourth largest natural satellite of Jupiter and sixth largest in the Solar System, Europa has been of interest to planetologists for many years. About forty years ago, the Voyager program provided the first detailed picture of the veined surface of the icy moon. In the last decades, the data collected on Europa has made it a priority target for space agencies in the search for life. And recently, planetologists have confirmed the presence of water vapor in Europe.

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What makes this moon so attractive is the possibility that it has all the ingredients necessary for life. Planetologists have evidence that one of these ingredients, liquid water, is present under the icy surface and can sometimes burst into space in the form of gigantic geysers. But so far no one has been able to confirm the presence of water in these plumes by directly detecting the water molecule.

Europa: water vapor and a potential ocean of liquid water

Now, an international research team led by NASA's Goddard Space Flight Center has directly detected water vapor for the first time over the surface of Europa. The team did this detection by surveying Europa through one of the largest telescopes in the world in Hawaii.

By confirming the presence of water vapor over Europa, planetologists can better understand the inner workings of the moon. For example, it helps to support the idea that there is an ocean of liquid water, perhaps twice as large as the Earth's, beneath the thick ice shell of that moon. Some astrophysicists suspect that another source of water for the plumes could be shallow reservoirs of melted water ice.

Although planetologists have still not surveyed the interior of Europe, the predominant hypothesis suggests the existence of an ocean of liquid water beneath its frozen surface. Credits: NASA

" The essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur) and energy sources, two of the three requirements of life, are present throughout the Solar System. But the third - liquid water - is a little hard to find beyond the Earth, "said Lucas Paganini, NASA's planetologist. " Although the scientists have not yet detected the liquid water directly, we have found the second best thing: water in the form of steam ."

First direct detection of water molecules over Europa

In Nature Astronomy , Paganini and his team said they detected enough water ejected from Europa (at a rate of 2360 kilograms per second) to fill an Olympic pool in minutes. However, the authors also discovered that water appears too rarely, at least in sufficient quantity, to be detected from Earth.

" For me, the interest of this work is not only the first direct detection of water over Europa, but also its absence within the limits of our detection method, " says Paganini.

Indeed, Paganini's team detected the weak but distinct signal of water vapor during 17 nights of observation between 2016 and 2017. Looking at the moon from WM Keck observatory at the top of Mauna Kea volcano in Hawaii, researchers have seen water molecules on the main hemisphere of Europa. (Europa, like the Earth's moon, is gravitationally locked on its host planet, so the main hemisphere is always oriented in the direction of the orbit, while the secondary hemisphere is always in the opposite direction).

Differentiate terrestrial water vapor from that of Europa: models in reinforcement

For this, the researchers used a Keck observatory spectrometer, which measures the chemical composition of planetary atmospheres by means of the infrared light they emit or absorb. Molecules such as water emit specific frequencies of infrared light when they interact with solar radiation.

When interacting with solar radiation, water molecules emit specific infrared frequencies. Credits: Michael Lentz / NASA Goddard

Detecting water vapor on other worlds is a challenge. Existing spacecraft have limited capabilities to detect it, and scientists using ground-based telescopes must take into account the distortion effects of the Earth's atmosphere.

To minimize this effect, Paganini's team used complex mathematical and computer modeling to simulate the conditions of the Earth's atmosphere, in order to differentiate between atmospheric water from Earth and Europa from the atmosphere. data returned by the Keck spectrograph.

We conducted rigorous safety checks to eliminate potential contaminants in ground observations, " said Avi Mandell, a planetologist on the Paganini team. " But in the end, we will have to get closer to Europa to see what is really happening ."

Structure of Europa: study it in detail thanks to the Europa Clipper mission

Scientists will soon be able to get close enough to Europa to resolve their outstanding questions about the internal and external functioning of this possibly habitable world. The next mission, Europa Clipper, which is scheduled for launch in the mid-2020s, will complete half a century of scientific discoveries that began with a modest photo.

When it arrives in Europa, the Clipper orbiter will carry out a detailed study of the surface, the deep interior, the weak atmosphere, the submarine ocean and possibly even smaller active vents. Clipper will try to take images of all the plumes and sample the molecules he will find in the atmosphere to study with his mass spectrometers. He will also look for a site from which a future lander could collect a sample.

In this video, NASA returns in detail on the detection of water vapor in Europa:


Article: A measurement of water vapour amid a largely quiescent environment on Europa

authors: L. Paganini, G. L. Villanueva, L. Roth, A. M. Mandell, T. A. Hurford, K. D. Retherford & M. J. Mumma

Nature Astronomy


Sunday, 17 November 2019

Another mystery on Mars: Oxygen appears and disappears without explanation

With the mystery of Mars methane still unresolved , the space robot Curiosity brought scientists a new puzzle: Martian oxygen.

The information came by measuring the seasonal levels of all gases in the atmosphere directly above the surface of the Gale Crater, where Curiosity is located. The result is disconcerting.

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On Mars, oxygen, the gas most creatures on Earth use to breathe, behaves in a way that scientists have so far failed to explain through any known chemical process.

Over the course of three Martian years (nearly six years of Earth), a Curiosity instrument called SAM ( Sample Analysis at Mars ) inhaled the air of the Gale Crater and analyzed its composition.

The results confirmed the composition of the Martian surface atmosphere: 95% by volume of carbon dioxide (CO2), 2.6% of molecular nitrogen (N2), 1.9% of argon (Ar), 0.16% of molecular oxygen. (O 2), and 0.06% carbon monoxide (CO).

Measurements also revealed how molecules in Martian air blend and circulate with changes in air pressure throughout the year. These changes are induced when CO2 gas freezes at the poles in winter, lowering air pressure across the planet after air redistribution to maintain pressure balance. When CO2 evaporates in spring and summer and mixes on Mars, the air pressure increases.

The oxygen mystery of Mars

In this environment, data show that nitrogen and argon follow a predictable seasonal pattern, with their concentration increasing and decreasing over the year relative to the amount of CO2 in the air.

Scientists expected oxygen to keep pace, but that is not the case. Instead, the amount of oxygen in the air rises throughout spring and summer by up to 30 percent, and then returns to the levels predicted by known autumn chemistry. This pattern repeats each spring, although the amount of oxygen added to the atmosphere varies, implying that something is producing oxygen and then taking it away.

"The first time we saw this, we were racking our brains," said Sushil Atreya, professor of climate and space science at the University of Michigan.

The team set out to look for possible explanations, first considering the possibility that CO2 or water (H2O) molecules could release oxygen when they separate into the atmosphere, leading to a brief rise in oxygen. But that would consume five times more water than there is in the atmosphere of Mars, and CO2 decomposes too slowly to generate it in such a short time. What about decreasing oxygen? Couldn't solar radiation break oxygen molecules into two atoms, which would then leak into space? No, the scientists concluded, as it would take at least 10 years for oxygen to disappear through this process.

"We are struggling to explain this," said Melissa Trainer, planetary scientist at NASA's Goddard Space Flight Center. "The fact that oxygen behavior doesn't repeat perfectly every season makes us think it's not a problem that has to do with atmospheric dynamics. It has to be a chemical source and a sinkhole that we can't yet explain."

The amount of oxygen in the air increases throughout spring and summer by up to 30 percent, and then returns to the levels predicted by known autumn chemistry

Methane and oxygen, biological and abiotic

The history of oxygen is curiously similar to the methane mystery of Mars. Methane is constantly in the air inside the Gale Crater in such small quantities (0.00000004% on average) that it almost goes unnoticed by the most sensitive instruments ever sent to Mars. Although methane increases and decreases seasonally, it increases abundantly by about 60% in the summer months for unexplained reasons - in fact, methane also fires randomly and dramatically, but no one has yet any idea why.

With the new oxygen discoveries at hand, the NASA team wonders if a chemistry similar to the one that is generating the natural seasonal variations of methane can also explain the variations in oxygen - the two gases even float together, but only occasionally.

"We are beginning to see this tantalizing correlation between methane and oxygen for much of the year on Mars," said Atreya. "I think there's something there. I don't have the answers yet. No one has."

Oxygen and methane can be produced biologically (from microbes, for example) and abiotically (from water and rock-related chemicals). Scientists are considering all options, although we have no convincing evidence of biological activity on Mars.

The Curiosity robot has no instruments that can definitely tell whether the source of methane or oxygen on Mars is biological or geological. With current data, nonbiological explanations are more likely.


Article: Seasonal variations in atmospheric composition as measured in Gale Crater, Mars

Authors: Melissa G. Trainer, Michael H. Wong, Timothy H. McConnochie, Heather B. Franz, Sushil K. Atreya, Pamela G. Conrad, Franck Lefèvre , Paul R. Mahaffy, Charles A. Malespin, Heidi LK Manning, Javier Martín-Torres, Germán M. Martínez, Christopher P. McKay, Rafael Navarro-González, Alvaro Vicente-Retortillo, Christopher R. Webster, Maria-Paz Zorzano

Magazine : Journal of Geophysical Research: Planets

DOI: 10.1029 / 2019JE006175  

Thursday, 14 November 2019

The Japanese space probe Hayabusa-2 returns to Earth with samples of an asteroid

Yesterday, the Japanese space probe Hayabusa-2 left its orbit around a distant asteroid and is now heading for the Earth after an exemplary mission. The latter will yield important samples, which could help scientists solve some of the mysteries about the origins of the Solar System.

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For the spacecraft, the long return journey began Wednesday, Nov. 13, 2019, and is expected to reach Earth "by the end of 2020," said Japan Aerospace Exploration Agency (JAXA).

"  We hope that Hayabusa-2 will provide us with new scientific knowledge, " said project director Yuichi Tsuda. The probe will bring back to Earth "carbon and organic matter", which will provide data on "how matter is dispersed in the solar system, why it exists on the asteroid and how it is related to the Earth", Tsuda added.

Below: The images taken by the Hayabusa-2 probe as it leaves the orbit of the asteroid are also displayed in the control room. This is a camera that continues to take scientifically valid photographs, but this time, the pictures were taken for the pleasure of all.

The mission of the Japanese space probe (the size of a large fridge) took her to some 300 million kilometers from the Earth, where she was able to analyze and explore the asteroid Ryugu, whose name means "Palace of Dragon "in Japanese. A name referring to a castle at the bottom of the ocean, in an ancient fable.

In April 2019, the Hayabusa-2 space probe launched an "impactor" on the asteroid in order to "stir" materials that had never been exposed to the atmosphere. The probe was then able to collect dust samples from the surface of the asteroid and never exposed to space vacuum so far. A first !

Scientists hope this will provide clues to the nature of the Solar System at birth, about 4.6 billion years ago. " I feel half-sad and half-determined, so we can do our best to bring the probe home. Ryugu has been at the heart of our daily lives for a year and a half ...  "said Tsuda.

The surface of the asteroid Ryugu, photographed in detail by the Hayabusa-2 probe at 64 and 67 meters altitude. Credits: JAXA

Now, the Hayabusa-2 space probe has begun its return to planet Earth. It will be released permanently from the gravity of the asteroid on November 18, and can start at full speed its main engines at the beginning of December.

Tsuda said the six-year mission, whose total cost is around 30 billion yen (about $ 278 million), had exceeded expectations at the scientific level, but he also admitted that his team had to deal with many technical problems. It took three and a half years for the probe to get to the asteroid, but the return trip should be much shorter because now the Earth and the Ryugu asteroid are much closer (because of their respective current positions).

The Hayabusa-2 probe is expected to deposit the collected samples in the southern Australian desert, but "JAXA is negotiating the details of this part of the mission with the Australian government," Tsuda said.

Note that this probe succeeds the first JAXA asteroid explorer, Hayabusa (which means "hawk" in Japanese). The first probe was sent back to Earth with dust samples of a small asteroid in 2010, despite several setbacks during its epic seven-year odyssey, and was hailed as a scientific triumph.

According to the current plan, Hayabusa-2 will continue its journey into space after depositing its capsule containing the samples on Earth, and could even " perform a new exploration of asteroid, " said spokesman JAXA Keiichi Murakami. "  The team has just started to study what could be done (after the probe has deposited the capsule), but there are no concrete plans for a new destination,  " Tsuda said.


We finally know more about what would have preceded the Big Bang

In the framework of the "pre-Big Bang" model, implying that the Big Bang is preceded by a first inflation, scientists theorize that the universe was formed in two stages. It would first spread rapidly from a dense mass of matter, then entered a phase of expansion more progressive but very energetic, commonly called "Big Bang". However, the way in which these two stages are related has long been misunderstood by researchers. As part of a new study of this period of the Universe and involving this initial theory, physicists finally think they have solved this mystery remained unanswered for decades, and suggest a way to explain the connection between these two eras primitive.

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During the first primitive period, the Universe would have gone from a small dense mass of matter to nearly a half-million times (x 10 48 ) its size in less than a trillionth of a second (10 -12 s) . In the context of the pre-Big Bang model, this period of rapid inflation was followed by a more gradual but violent expansion phase, the Big Bang.

During the Big Bang, a "ball" of extremely hot matter composed of fundamental particles (protons, neutrons and electrons ) then developed and cooled to form the first atoms, stars and galaxies .

The standard Big Bang theory , which also describes cosmic inflation, remains the most widely supported explanation for the beginnings of our universe. However, scientists are still puzzled as to how these completely different expansion periods are nested.

To solve this mystery, a team of researchers from Kenyon College, the Massachusetts Institute of Technology (MIT) and the University of Leiden in the Netherlands, simulated the critical transition between cosmic inflation and the Big Bang as part of a pre-Big Bang model; a period called "reheat".

" The post-inflation warm-up period defines the conditions of the Big Bang and, in a sense, places the 'Bang' in the Big Bang,  " David Kaiser, a professor of physics at MIT , said in a statement . " It's a time of transfer, when hell is unleashed and the matter behaves in a complex way  ."

The history of the universe (standard model of the Big Bang). Above, inflation, which generates two types of waves: gravitational waves and density waves. Below, the radius of the visible Universe, from the Big Bang (t0), then the inflation (white / yellow), the formation of the protons, the beginning of the nuclear fusion, the end of the nuclear fusion (3 minutes), up to the 13.8 billion years that the Universe has today. Credits: DrBogdan / Yinweichen / Wikimedia

When the Universe developed into a "fraction of a second" during cosmic inflation, all existing matter spread out in all directions, leaving in space an empty, cold place, devoid of "soup." primordial "(dense and hot cluster of particles) necessary to start the Big Bang. During the warm-up period, it is thought that the energy that propelled inflation broke down into particles, said Rachel Nguyen, PhD student in physics at the University of Illinois and lead author of the study.

Once these particles are produced, they bounce off and bump into each other, transferring inertia and energy,  " Nguyen said. " And this is what thermises and warms the universe to define the initial conditions of the Big Bang  ".

In their model, Nguyen and his colleagues simulated the behavior of an exotic form of matter called inflaton. Scientists believe that the scalar field of this material, which is similar in nature to that of the Higgs boson, is responsible for creating the energy field that has led to cosmic inflation.

Their model showed that, under proper conditions, the hypothetical scalar field energy could be efficiently redistributed to create the diversity of particles needed to warm the primitive Universe. The results of the study are available in Physical Review Letters.

Gravity: it would react differently to very high energies

" When we study the primitive universe, we perform an experiment with particles at very high temperatures,  " said Tom Giblin, an associate professor of physics at Kenyon College in Ohio and co-author of the study. " The transition from the cold inflationary period to the warm period should contain essential evidence about the particles that actually exist at these extremely high energies."

A fundamental question that still afflicts physicists is how gravity behaves to the extreme energies present during inflation. Albert Einstein's theory of general relativity defines that all matter is affected by gravity in the same way, where the force of gravity is constant, regardless of the energy of the particle. However, because of the strange properties of quantum mechanics, scientists now think that at very high energies matter reacts differently to gravity.

The team incorporated this hypothesis into their model by modifying the interaction force of particles with gravity. They then discovered that the more they increased the force of gravity, the more the inflaton effectively transferred energy to produce the Hot Bang's field of hot material particles.

Additional clues needed to support the model

" The universe contains so many secrets, encoded in a very complex way  ," said Giblin. " It's our job to study the nature of reality by offering a 'decoding device' - a way to extract information from the universe. For this, we use simulations to predict what the universe should look like, so that we can actually begin to decode it. This warm-up period should have left an imprint somewhere. We just have to find it  . "

But identifying this footprint could prove to be a very complex task. Our first glimpse of the Universe is a "bubble of radiation" left a few hundred thousand years after the Big Bang: the cosmic microwave background (CMB). However, the CMB only evokes the state of the universe during the first critical seconds of its birth. Physicists hope that future observations of gravitational waves will provide the additional clues needed to support their model.


Thursday, 7 November 2019

A new study suggests that the Universe is actually spherical and closed (not flat)

The study of the curvature of the Universe is an active field of research in cosmology. In recent years, the many data collected by observation missions such as WMAP and Planck have shown a locally null curvature of the Universe, indicating that the latter is certainly flat. The data match so well with each other that the model of the flat Universe is today integrated into the standard cosmological model. However, an anomaly derived from data collected by the Planck Space Observatory in 2018, concerning the cosmic microwave background, could be interpreted as a sign of a closed spherical universe.

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On the basis of data collected last year by the Planck satellite of the European Space Agency, cosmologists have argued that the Universe is actually curved and closed, like an expanding sphere. This means that a beam of photons drawn in a straight line would eventually return to its starting point, crossing other beams in its path; whereas these beams would remain parallel in the scenario of the flat Universe.

According to an international team of astronomers led by Eleonora Di Valentino of the University of Manchester in the United Kingdom, their findings present a "cosmological crisis" that calls for "radical rethinking of the current model of cosmological concordance". The key in determining the curvature of the Universe lies in the way gravity curves the path of light, an effect predicted by Einstein and called the gravitational lens .

Unlike a flat Universe (zero curvature) where light beams would continue indefinitely their stroke in a straight line, in a closed Universe (positive curvature), they would eventually return to their starting point. Credits: Lucy Reading-Ikkanda

Anomaly A lens : it could be explained by a closed sphere Universe

It is not about any light but the cosmic microwave background (CMB), that is to say the electromagnetic radiation bathing the Universe, whose first emission dates back to 380,000 years after the Big Bang during a phase called Recombination (capture of electrons by atomic nuclei).

The Planck satellite data, particularly from 2018, show that CMB has a more pronounced gravitational lens effect than expected. The Planck Collaboration has called this anomaly A lens , and this has not yet been resolved, but the team believes that an explanation could be the curvature of the Universe. The study was published in the journal Nature Astronomy.

The researchers showed that the anomaly in the spectrum of the cosmic microwave background could be interpreted as the sign of a closed universe (blue). Credits: Eleonora Di Valentino et al. 2019

"A closed universe can provide a physical explanation for this, with the Planck CMB spectrum now pointing to a positive curvature of greater than 99% confidence. Here we study further evidence of a closed universe collected by Planck, showing that positive curvature naturally explains the abnormal amplitude of the lens effect, "the researchers write.

An interpretation incompatible with all current data

A curved universe may explain this anomaly, but there are several important issues, including the fact that all other analyzes of Planck datasets, including the same data from 2018, concluded that the standard cosmological model is correct, including concerning a flat universe.

There are also other problems, and the team took care to note them in its article. One is Hubble's constant, which gives the rate of expansion of the Universe; it is a real problem in cosmology today. The different measures of this constant give different values, and to consider a curved universe makes this measurement even more complex.

The interpretation of the authors of the article (red and blue) is incompatible with the current data from different missions of cosmological observation (gray). Credits: Eleonora Di Valentino et al. 2019

Data from baryonic acoustic oscillation studies on dark energy are also inconsistent with the Closed Universe model, as are data on gravitational distortion obtained from observations of weak gravitational lenses . One other article also suggests that the anomaly A lens is simply a statistical bias in the data collected.

Future studies are needed to clarify the nature of the anomaly

Astrophysicists George Efstathiou and Steven Gratton of the University of Cambridge also analyzed Planck's 2018 data and found signs of curvature. But when compared to other Planck data sets and baryonic acoustic oscillations data, they found "solid evidence to support a spatially flat universe".

Much of the data seems to be in favor of a flat universe rather than a closed universe, except for the anomaly A lens . " Future steps will be needed to clarify whether the observed discrepancies are due to undetected systematics, new physics, or simply statistical fluctuation, " the researchers conclude.