Earth’s Atmosphere Stretches Out To The Moon – And Beyond

The gaseous layer that wraps around Earth reaches up to 630,000 kilometers away, or 50 times the diameter of our planet, according to a new study based on observations by the ESA/NASA Solar and Heliospheric Observatory, SOHO, and published in AGU’s Journal of Geophysical Research: Space Physics.

“The moon flies through Earth’s atmosphere,” says Igor Baliukin of Russia’s Space Research Institute, lead author of the paper presenting the results. “We were not aware of it until we dusted off observations made over two decades ago by the SOHO spacecraft.”

Where our atmosphere merges into outer space, there is a cloud of hydrogen atoms called the geocorona. One of the spacecraft instruments, SWAN, used its sensitive sensors to trace the hydrogen signature and precisely detect how far the very outskirts of the geocorona are. These observations could be done only at certain times of the year, when the Earth and its geocorona came into view for SWAN.

For planets with hydrogen in their exospheres, water vapor is often seen closer to their surface. That is the case for Earth, Mars and Venus.

“This is especially interesting when looking for planets with potential reservoirs of water beyond our solar system,” explains Jean-Loup Bertaux, co-author and former principal investigator of SWAN.

The first telescope on the moon, placed by Apollo 16 astronauts in 1972, captured an evocative image of the geocorona surrounding Earth and glowing brightly in ultraviolet light.

“At that time, the astronauts on the lunar surface did not know that they were actually embedded in the outskirts of the geocorona,” says Jean-Loup.

Cloud of hydrogen
The sun interacts with hydrogen atoms through a particular wavelength of ultraviolet light called Lyman-alpha, which the atoms can both absorb and emit. Since this type of light is absorbed by Earth’s atmosphere, it can only be observed from space.

Thanks to its hydrogen absorption cell, the SWAN instrument could selectively measure the Lyman-alpha light from the geocorona and discard hydrogen atoms further out in interplanetary space.

The new study revealed that sunlight compresses hydrogen atoms in the geocorona on Earth’s dayside, and also produces a region of enhanced density on the night side. The denser dayside region of hydrogen is still rather sparse, with just 70 atoms per cubic centimeter at 60,000 kilometers above Earth’s surface, and about 0.2 atoms at the moon’s distance.

“On Earth we would call it vacuum, so this extra source of hydrogen is not significant enough to facilitate space exploration,” says Igor. The good news is that these particles do not pose any threat for space travelers on future crewed missions orbiting the moon.

“There is also ultraviolet radiation associated to the geocorona, as the hydrogen atoms scatter sunlight in all directions, but the impact on astronauts in lunar orbit would be negligible compared to the main source of radiation – the sun,” says Jean-Loup Bertaux.

On the down side, the Earth’s geocorona could interfere with future astronomical observations performed in the vicinity of the moon.

“Space telescopes observing the sky in ultraviolet wavelengths to study the chemical composition of stars and galaxies would need to take this into account,” adds Jean-Loup.
The power of archives

Launched in December 1995, the SOHO space observatory has been studying the sun, from its deep core to the outer corona and the solar wind, for over two decades. The satellite orbits around the first Lagrange point (L1), some 1.5 million kilometers from Earth towards the sun.

This location is a good vantage point to observe the geocorona from outside. SOHO’s SWAN instrument imaged Earth and its extended atmosphere on three occasions between 1996 and 1998.

Jean-Loup and Igor’s research team in Russia decided to retrieve this data set from the archives for further analysis. These unique views of the whole geocorona as seen from SOHO are now shedding new light on Earth’s atmosphere.

“Data archived many years ago can often be exploited for new science,” says Bernhard Fleck, ESA SOHO project scientist. “This discovery highlights the value of data collected over 20 years ago and the exceptional performance of SOHO.”

Cosmic Dust Forms On Supernovae Blasts

Scientists claim to have solved a longstanding mystery as to how cosmic dust, the building blocks of stars and planets, forms across the Universe.

Cosmic dust contains tiny fragments or organic material and is spread out across the Universe. The dust is primarily formed in stars and is then blown off in a slow wind or a massive star explosion.

Up until now, astronomers have had little understanding as to why so much cosmic dust exists in the interstellar medium, with theoretical estimates suggesting it should be obliterated by supernova explosions.

A supernova is an event that occurs upon the violent death of a star and is one of the most powerful events in the Universe, producing a shockwave which destroys almost anything in its path.

Yet new research published in the Monthly Notices of the Royal Astronomical Society has observed the survival of cosmic dust around the closest supernova explosion detected to us, Supernova 1987A.

Observations using NASA’s research aircraft, the Stratospheric Observatory for Infrared Astronomy (SOFIA), have detected cosmic dust in a distinctive set of rings that form part of Supernova 1987A.

The results seem to suggest that there is rapid growth of cosmic dust within the rings, leading the team to believe that dust may actually be re-forming after it is destroyed in the wake of a supernova blast wave.

This immediacy – that the post-shock environment might be ready to form or re-form dust – had never been considered before, and may be pivotal in fully understanding how cosmic dust is both created and destroyed.

“We already knew about the slow-moving dust in the heart of 1987A,” said Dr. Mikako Matsuura, lead author on the paper from the School of Physics and Astronomy.

“It formed from the heavy elements created in the core of the dead star. But the SOFIA observations tell us something completely new.”

Cosmic dust particles can be heated from tens to hundreds of degrees causing them to glow at both infrared and millimeter wavelengths. Observations of millimeter-wave dust emission can generally be carried out from the ground using telescopes; however, observations in the infrared are almost impossible to interference from the water and carbon dioxide in the Earth’s atmosphere.

By flying above most of the obscuring molecules, SOFIA provides access to portions of the infrared spectrum not available from the ground.

Solar Mystery Starts To Unravel As NASA Detects ‘Tadpole’ Jets Coming From Sun’s Surface

One of the biggest mysteries of the Sun is why its upper atmosphere—also known as the corona—is over 200 times hotter than its surface. For some unknown reason, this region that extends millions of miles into space is superheated—while the surface temperature hovers around 5,500 degree Celsius, the corona can reach two million degrees Celsius.

In a study published in Nature Astronomy, scientists with NASA are now edging closer to understanding this weird phenomenon.

While analyzing data taken by one of the space agency’s solar observation satellites, researchers discovered jets emerging from sunspots and shooting up to 3,000 miles into the inner corona. The jets had bulky heads and slim tails, so they looked like tadpoles swimming through the layers of the Sun.

Sunspots are regions that temporarily appear on the surface of the Sun. They are much cooler than the surrounding areas and are highly magnetized.

Previously, there were two main hypotheses about what was heating the Sun’s corona. The first relates to nanoflares, where explosions caused by the reconnection of magnetic lines release energy into the atmosphere, heating it in the process. The second involves electromagnetic waves, with charged particles being pushed into the Sun’s atmosphere. The tadpole discovery adds a third possibility to the mix.

Scientists found the tadpoles were made up entirely of plasma—the fourth state of matter, consisting of electrically conducting material made up of charged particles. The tadpoles (also known as ‘pseudo shocks’) may help heat up the Sun’s corona at specific times in its 11 year cycle—specifically during the solar maximum, when there is increased activity on the Sun’s surface.

The pseudo-shocks are thought to occur when magnetic field lines become tangled and produce explosions. This often happens around sunspots, but may well take place in other magnetized regions of space.

Computer simulations showed that the tadpoles could carry enough energy to heat the inner corona.

“We were looking for waves and plasma ejecta, but instead, we noticed these dynamical pseudo-shocks, like disconnected plasma jets, that are not like real shocks but highly energetic to fulfill Sun’s radiative losses,” lead author Abhishek Srivastava, from Indian Institute of Technology, said in a statement.

The Sun is currently coming to the end of its latest cycle—known as sunspot cycle 24—and will enter the next one at some point this year. As the new cycle begins, sunspot activity will begin to increase before reaching a peak, known as the solar maximum—currently expected to be around 2024.

Previously, scientists suggested that sunspot cycle 25 could be weaker than the current cycle, potentially meaning a period of global cooling could ensue. However, this has largely been ruled out, with a team of scientists in India recently predicting that the next solar cycle could be even stronger than the current one.

In their paper published in Nature Astronomy, the authors said: “We conclude that near-Earth and inter-planetary space environmental conditions and solar radiative forcing of climate over sunspot cycle 25 (i.e., the next decade) will likely be similar or marginally more extreme relative to what has been observed during the past decade over the current solar cycle.”

Huge Winter Storm Moves East: Snow, Sleet, Heavy Rain Target 39 States

ARLINGTON, Va. – A blanket of snow and ice descended on a wide swath of the nation’s northern tier Wednesday as a mammoth winter storm affecting every state east of the Mississippi River left a trail of closures and travel headaches.

While the Central Plains saw the bulk of its snow in the overnight hours, cities including Detroit, Chicago, Philadelphia, New York and Washington were getting the worst of the storm on Wednesday.

Airline traffic was under siege, with almost 700 flights canceled into and out of metro Washington’s three airports alone by 7 a.m. More than 205 were canceled and about the same number delayed at Chicago’s O’Hare, Philadelphia International had more than 120 flights canceled.

The storm is expected to end Thursday, but not before affecting more than 200 million people.

The National Weather Service’s local forecast for parts of Virginia on Wednesday was several inches of snow followed by ice and sleet. It’s warning of dangerous conditions was a recurring theme across much of the nation.

“Travel will be very difficult. The hazardous conditions will impact the morning and evening commutes,” the notice said. “The combined weight of snow, sleet and freezing rain could result in downed branches and isolated power outages.”

In Washington, D.C., federal offices were closed although emergency staff and teleworkers remained on the job.

School closing in major cities and their environs stretched from Minneapolis down to Kansas City and east to Washington and Philadelphia.

In suburban Arlington, the school schedule has been plagued by a string of closures and late openings all winter. High school math teacher Bill Drake was preparing to begin digging out amid heavy snowfall that was forecast to turn to ice.

“I love snow days as much as the kids,” Drake said. “It’s hard to make up for missed time in the classroom, but the extra time with my family is a huge bonus.”

Officials scheduled vehicle restrictions on Pennsylvania highways Wednesday, urging people to monitor snow and ice.

Daily snowfall records were set on Tuesday in North Little Rock, Arkansas; and Omaha and Lincoln, Nebraska; all of which received several inches of snow, AccuWeather reported.

A quarter-inch of ice weighed down branches and power lines in Boone County, Arkansas, knocking out power for 2,000 households on Tuesday night. Car accidents and road closures also paralyzed parts of Nebraska, Kansas, Missouri and Iowa, AccuWeather said.

On Wednesday, 4 to 8 inches of snow was expected from eastern Nebraska into eastern Minnesota and northwestern Wisconsin. Temperatures will be below freezing from the Dakotas into the Upper Mississippi Valley through Thursday, the National Weather Service said.

The Mid-Atlantic will see snow change to sleet and freezing rain, followed by rain. Areas near the central Appalachians may see 4 to 8 inches of snow and ice accumulations up to 0.25 inches.

In the South, an additional 1 to 3 inches of heavy rain will fall on already saturated grounds through Wednesday afternoon. The National Weather service has issued flood and flash flood watches from the Lower Mississippi Valley into portions of the Ohio Valley.

West of the Rocky Mountains, the National Weather Service said high temperatures will be 10 to 20 degrees below average through Thursday. More than a foot of snow is expected through Thursday night in some of the major mountain ranges from Washington and Oregon into Arizona and southwestern Colorado.

LOFAR Radio Telescope Reveals Secrets Of Solar Storms

An international team of scientists led by a researcher from Trinity College Dublin and University of Helsinki announced a major discovery on the very nature of solar storms in the journal Nature Astronomy.

The team showed that solar storms can accelerate particles simultaneously in several locations by combining data from the Low Frequency Array, LOFAR, with images from NASA, NOAA and ESA spacecraft.

The sun is the closest star to Earth, and like many stars, it is far from quiet. Sunspots many times the size of Earth can appear on its surface and store enormous reservoirs of energy. And it is within these regions that huge explosions called solar storms occur. Solar storms are spectacular eruptions of billions of tonnes of hot gas traveling at millions of kilometres an hour. The Nature Astronomy paper reports on a particularly large solar storm that occured on September 10, 2017, soon after the LOFAR station in Ireland came online.

How to predict space weather

“Our results are very exciting, as they give us an amazingly detailed insight into how solar storms propagate away from the sun and where they accelerate fast particles with speeds close to the speed of light,” says Dr. Diana Morosan, the lead author on the publication, and affiliated with Trinity College Dublin and the University of Helsinki.

These results may in the future help researchers to produce more accurate forecasts of solar radio bursts and determine how solar storms impact the Earth—they can produce beautiful displays of the aurora, but they can also cause problems with communication and navigation systems and power grids. Society is now even more dependent on technology, and solar storms have the potential to cause significant effects on their performance.

In 1859, the largest solar storm ever observed – the so-called Carrington Event – occurred. Within hours, it generated displays of aurora as far south as Italy and Cuba and caused interruptions in early telegraph systems in Europe and the U.S.

During a 2003 event, transformers in South Africa were damaged, and Swedish air traffic control systems were closed down in 2015 for more than an hour due to effects associated with a solar storm. More than 50 satellites reported problems. More recently, emergency response communications were interrupted during hurricane season in September 2017 in the Caribbean.

“We used data from the Low Frequency Array, LOFAR, together with images from NASA, NOAA and ESA spacecraft to show where solar storms accelerate fast particles,” says Morosan.

Spacecraft Measurements Reveal Mechanism Of Solar Wind Heating

Queen Mary University of London has led a study which describes the first direct measurement of how energy is transferred from the chaotic electromagnetic fields in space to the particles that make up the solar wind, leading to the heating of interplanetary space.

The study, published in Nature Communications and carried out with University of Arizona and the University of Iowa, shows that a process known as Landau damping is responsible for transferring energy from the electromagnetic plasma turbulence in space to electrons in the solar wind, causing their energisation.

This process, named after the Nobel-prize winning physicist Lev Landau (1908-1968), occurs when a wave travels through a plasma and the plasma particles that are travelling at a similar speed absorb this energy, leading to a reduction of energy (damping) of the wave.

Although this process had been measured in some simple situations previously, it was not known whether it would still operate in the highly turbulent and complex plasmas occurring naturally in space, or whether there would be a different process entirely.

All across the universe, matter is in an energised plasma state at far higher temperatures than expected. For example, the solar corona is hundreds of times hotter than the surface of the Sun, a mystery which scientists are still trying to understand.

It is also vital to understand the heating of many other astrophysical plasmas, such as the interstellar medium and the disks of plasma surrounding black holes, in order to explain some of the extreme behaviour displayed in these environments.

Being able to make direct measurements of the plasma energisation mechanisms in action in the solar wind (as shown in this paper for the first time) will help scientists to understand numerous open questions, such as these, about the universe.

The researchers discovered this using new high-resolution measurements from NASA’s Magnetospheric Multi-Scale (MMS) spacecraft (recently launched in 2015), together with a newly-developed data analysis technique (the field-particle correlation technique).

The solar wind is the stream of charged particles (i.e., plasma) that comes from the Sun and fills our entire solar system, and the MMS spacecraft are located in the solar wind measuring the fields and particles within it as it streams past.

Lead author Dr Christopher Chen, from Queen Mary University of London, said: “Plasma is by far the most abundant form of visible matter in the universe, and is often in a highly dynamic and apparently chaotic state known as turbulence. This turbulence transfers energy to the particles in the plasma leading to heating and energisation, making turbulence and the associated heating very widespread phenomena in nature.

“In this study, we made the first direct measurement of the processes involved in turbulent heating in a naturally occurring astrophysical plasma. We also verified the new analysis technique as a tool that can be used to probe plasma energisation and that can be used in a range of follow-up studies on different aspects of plasma behaviour.”

University of Iowa’s Professor Greg Howes, who co-devised this new analysis technique, said: “In the process of Landau damping, the electric field associated with waves moving through the plasma can accelerate electrons moving with just the right speed along with the wave, analogous to a surfer catching a wave. This first successful observational application of the field-particle correlation technique demonstrates its promise to answer long-standing, fundamental questions about the behavior and evolution of space plasmas, such as the heating of the solar corona.”

This paper also paves the way for the technique to be used on future missions to other areas of the solar system, such as the NASA Parker Solar Probe (launched in 2018) which is beginning to explore the solar corona and plasma environment near the Sun for the first time.

Gravitational Waves Will Settle Cosmic Conundrum

Measurements of gravitational waves from approximately 50 binary neutron stars over the next decade will definitively resolve an intense debate about how quickly our universe is expanding, according to findings from an international team that includes University College London (UCL) and Flatiron Institute cosmologists.

The cosmos has been expanding for 13.8 billion years. Its present rate of expansion, known as “the Hubble constant,” gives the time elapsed since the Big Bang.

However, the two best methods used to measure the Hubble constant have conflicting results, which suggests that our understanding of the structure and history of the universe — the “standard cosmological model” — may be incorrect.

The study, published today in Physical Review Letters, shows how new independent data from gravitational waves emitted by binary neutron stars called “standard sirens” will break the deadlock between the conflicting measurements once and for all.

“We’ve calculated that by observing 50 binary neutron stars over the next decade, we will have sufficient gravitational wave data to independently determine the best measurement of the Hubble constant,” said lead author Dr. Stephen Feeney of the Center for Computational Astrophysics at the Flatiron Institute in New York City. “We should be able to detect enough mergers to answer this question within five to 10 years.”

The Hubble constant, the product of work by Edwin Hubble and Georges Lemaître in the 1920s, is one of the most important numbers in cosmology. The constant “is essential for estimating the curvature of space and the age of the universe, as well as exploring its fate,” said study co-author UCL Professor of Physics & Astronomy Hiranya Peiris.

“We can measure the Hubble constant by using two methods — one observing Cepheid stars and supernovae in the local universe, and a second using measurements of cosmic background radiation from the early universe — but these methods don’t give the same values, which means our standard cosmological model might be flawed.”

Feeney, Peiris and colleagues developed a universally applicable technique that calculates how gravitational wave data will resolve the issue.

Gravitational waves are emitted when binary neutron stars spiral toward each other before colliding in a bright flash of light that can be detected by telescopes. UCL researchers were involved in detecting the first light from a gravitational wave event in August 2017.

Binary neutron star events are rare, but they are invaluable in providing another route to track how the universe is expanding. The gravitational waves they emit cause ripples in space-time that can be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo experiments, giving a precise measurement of the system’s distance from Earth.

By additionally detecting the light from the accompanying explosion, astronomers can determine the system’s velocity, and hence calculate the Hubble constant using Hubble’s law.

For this study, the researchers modelled how many such observations would be needed to resolve the issue of measuring the Hubble constant accurately.

“This in turn will lead to the most accurate picture of how the universe is expanding and help us improve the standard cosmological model,” concluded Professor Peiris.

The study involved researchers from the Flatiron Institute (USA), UCL, Stockholm University, Radboud University (The Netherlands), Imperial College London, and the University of Chicago. UCL’s contribution was generously funded by the European Research Council.