Vega lofts two satellites on second launch this year

ARIANESPACE - Flight VV10 Mission poster.


2 August 2017

This morning Arianespace launched a Vega rocket carrying two Earth observation satellites for Italy, France and Israel encased in Vega’s lighter protective fairing.

Vega liftoff

Liftoff of Vega’s 10th mission from Europe’s Spaceport in Kourou, French Guiana came at 01:58 GMT on 2 August (03:58 CEST; 22:58 local time on 1 August) on a mission lasting 97 minutes to deliver Optsat-3000 and Venμs into their planned orbits.

Optsat-3000 will provide Italy’s Ministry of Defense with global high-resolution images. With a mass of 368 kg, it was the first to be released after about 42 minutes. The 264 kg Venμs was released 49 minutes later.

Perfect 10: the lightweight Vega orbits OPTSAT-3000 and Venµs on a milestone success

Venμs – Vegetation and Environment monitoring on a New Micro Satellite – sponsored by France and Israel will study vegetation and the environment, and demonstrate a new electrical propulsion system.

Optsat-3000 has a design life of seven years and Venμs four and a half years.

Optsat-3000 satellite

Flight VV10 marks the debut of Vega’s new lighter payload fairing that protects the satellites during the ascent to space. It was developed under ESA’s Launchers Exploitation Accompaniment Programme and manufactured by RUAG Space Switzerland with ELV in Italy as prime contractor. The technology was first proved on 28 June on Ariane 5.

The new Vega fairing structure features fewer panels and no metallic joints. Different composite material and improved manufacturing have lowered the production cost.

A launch pad modification for this flight reduced the acoustic loads – the pressure caused by sound waves on the payloads at liftoff – from the first-stage plume striking the structure.

Venμs – Vegetation and Environment monitoring on a New Micro Satellite

The changes exploited a computer model of the acoustic environment at liftoff developed under an ESA–NASA knowledge exchange agreement for launchers. Flight and ground measurements from this flight will help to gauge the improvements.

The payload mass for this launch was about 982 kg. The satellites totalled about 672 kg, with payload adapters and carrying structures making up the rest.

Related links:

Vega rocket: http://www.esa.int/Our_Activities/Space_Transportation/Launch_vehicles/Vega

Arianespace: http://www.arianespace.com/

ELV SpA: http://www.elv.it/en/

NASA: https://www.nasa.gov/

RUAG Space Switzerland: http://www.ruag.com/space/RUAG_Space_Switzerland

Images, Video, Text, Credits: ESA/ARIANESPACE.


Best regards, Orbiter.ch

New Supersonic Technology Designed to Reduce Sonic Booms

NASA logo.

Aug. 1, 2017

NASA’s F-18 test aircraft. Image Credit: NASA

Residents along Florida's Space Coast will soon hear a familiar sound -- sonic booms. But instead of announcing a spacecraft's return from space, they may herald a new era in faster air travel.

NASA's Kennedy Space Center in Florida is partnering with the agency's Armstrong Flight Research Center in California, Langley Research Center in Virginia, and Space Florida for a program called Sonic Booms in Atmospheric Turbulence, or SonicBAT II. Starting in mid-August, NASA F-18 jets will take off from the Shuttle Landing Facility (SLF) and fly at supersonic speeds while agency researchers on the ground measure the effects of low-altitude turbulence on sonic booms.

The project is another example of Kennedy's role as a premier, multi-user spaceport. In 2015, the center signed a 30-year property agreement with Space Florida for the operations and management of the SLF. This partnership provides an avenue for a variety of commercial and government partners to have access to use the three-mile long runway.

According to John Graves of NASA Flight Operations in Kennedy's Spaceport Integration and Services, for projects such as SonicBAT, NASA coordinates with Space Florida who manages the facility's schedule.

Image above: NASA’s F-18 will fly at or above 32,000 feet when it goes supersonic off the eastern coast of Florida. The F-18’s flightpath is positioned in efforts to keep the strongest-sounding sonic booms away from residential areas, while still producing sonic booms over the Kennedy Space Center, where the sonic boom sound will be collected by microphone arrays on the ground. While sonic booms will be more audible on the beaches north of Kennedy, Cape Canaveral Air Force Station will hear “muted,” or quieter, sonic booms. Areas including Scottsmoor, Mims, Titusville, Port St. John, Cocoa, and Port Canaveral are likely to hear a sound closer to the rumble of distant thunder, though people may hear an occasional “muted” sonic boom. Image Credit: NASA.

"Working with representatives from the Armstrong center, we go through Space Florida to request use of the runway," he said. "It's an arrangement that works very well."

The F-18 will begin flights on Aug. 21, flying two to four times a day over a period of ten days. But the actual test window may be two weeks to allow for weather and other possible delays.

Graves explains that SonicBAT is an unusual test in that it uses a typical military aircraft with its loud sonic boom to help engineers better understand the sounds from future quiet supersonic aircraft

"We're hoping we can eventually lower sonic booms to a low rumble," he said. "The goal is to eventually accommodate jets that can fly from New York to Los Angeles in two hours."

Armstrong started SonicBAT investigations at Edwards Air Force Base last year. This will be the second round of tests.

"Edwards is a hot, dry environment," he said. "The team at the Armstrong center wants to now try to collect similar data in the hot, humid climate we have here."

The problem is sonic booms are bothersome, loud, thunder-like sounds occurring when an aircraft or other aerospace vehicle flies overhead faster than the speed of sound -- about 767 mph. U.S. Air Force pilot Chuck Yeager was the first to break the sound barrier on Oct. 14, 1947, at Muroc (now Edwards) Air Force Base in California.

Throughout the 1950s and 1960s, sonic booms became a familiar part of American life as military jets became faster and faster. At the time, it seemed that supersonic passenger air travel was on the near horizon. However, the boom created by shock waves, or rapid changes in pressure that occur at supersonic speeds, disturbed people and occasionally caused property damage when military aircraft flew at very low altitudes. Consequently, such flights currently are restricted by the Federal Aviation Administration, except for craft such as the now-retired space shuttle, SpaceX Falcon 9 first stages and the X-37B Orbital Test Vehicle.

Image above: One of three microphone arrays positioned strategically along the ground at Edwards Air Force Base, California, sits ready to collect sound signatures from sonic booms created by a NASA F-18 during the SonicBAT flight series. Similar arrays will be set up near NASA's Kennedy Space Center to collect the sound signatures of booms that have traveled through atmospheric turbulence before reaching the ground. Image Credits: NASA/Lauren Hughes.

"For the upcoming tests, F-18 jets will fly offshore from Daytona at about 41,000 feet," Graves said. "They will fly south, diving down below to around 32,000 feet and accelerating to supersonic speeds to create a sonic boom that will reach the ground where the test equipment is located."

There will be a small motorized glider which can fly with its engine off positioned above the 14,000-foot level to measure sonic booms above the turbulent layer, and microphone sensors set up north and south of Launch Complex 39B.

With this data and building on previous supersonic research, NASA hopes to develop cutting-edge tools and technologies for the design of future "low boom" aircraft reducing or almost eliminating the noise.

Image above: This illustration depicts NASA’s planned Low Boom Flight Demonstration aircraft. The agency and Lockheed Martin have just completed the preliminary design of the Quiet Supersonic Transport, or QueSST, aircraft studying the shape and position of aircraft components, along with the propulsion system to determine what factors contributes to an aircraft’s sonic boom. Image Credits: NASA/Lockheed Martin.

The ongoing research goes beyond SonicBAT. NASA and partners in U.S. industry and universities are testing a variety of factors that may make supersonic passenger travel a reality. The next exciting step will be the development of experimental aircraft that can demonstrate low boom flight. NASA and Lockheed Martin have just completed the preliminary design of the Quiet Supersonic Transport, or QueSST, aircraft studying the shape and position of aircraft components, along with the propulsion system to determine what factors contribute to an aircraft’s sonic boom.

In the next phase of this effort, NASA will partner with U.S. industry to build the Low Boom Flight Demonstrator, an experimental aircraft that, when flying at supersonic speeds, will create a soft “thump” instead of the disruptive sonic boom.

Related links:

Armstrong Flight Research Center: https://www.nasa.gov/centers/armstrong/home/index.html

Langley Research Center: https://www.nasa.gov/langley

Sonic Booms in Atmospheric Turbulence (SonicBAT): https://www.nasa.gov/centers/armstrong/features/flights_study_atmospheric_effect_on_sonic_booms.html

Quiet Supersonic Transport (QueSST): https://www.nasa.gov/press-release/nasa-completes-milestone-toward-quieter-supersonic-x-plane

Supersonic Flight: https://www.nasa.gov/subject/7566/supersonic-flight

Images (mentioned), Text, Credits: NASA's Kennedy Space Center, by Bob Granath.

Greetings, Orbiter.ch

NASA Continues to Study Pulsars, 50 Years After Their Chance Discovery

NASA - NICER - SEXTANT Mission patch.

Aug. 1, 2017

Pulsar. Image Credits: NASA’s Goddard Space Flight Center

A little bit of “scruff” in scientific data 50 years ago led to the discovery of pulsars – rapidly spinning dense stellar corpses that appear to pulse at Earth.

Astronomer Jocelyn Bell made the chance discovery using a vast radio telescope in Cambridge, England. Although it was built to measure the random brightness flickers of a different category of celestial objects called quasars, the 4.5-acre telescope produced unexpected markings on Bell’s paper data recorder every 1.33730 seconds. The pen traces representing radio brightness revealed an unusual phenomenon.

“The pulses were so regular, so much like a ticking clock, that Bell and her supervisor Anthony Hewish couldn’t believe it was a natural phenomenon,” said Zaven Arzoumanian of NASA's Goddard Space Flight Center in Greenbelt, Maryland. “Once they found a second, third and fourth they started to think differently.”

The unusual stellar objects had been previously predicted but never observed. Today, scientists know of over 2,000 pulsars. These rotating “lighthouse” neutron stars begin their lives as stars between about seven and 20 times the mass of our sun. Some are found to spin hundreds of times per second, faster than the blades of a household blender, and they possess enormously strong magnetic fields.

Animation above: Most known neutron stars are observed as pulsars, emitting narrow, sweeping beams of radiation. They squeeze up to two solar masses into a city-size volume, crushing matter to the highest possible stable densities. To explore these exotic states of matter, NICER measures X-ray emissions across the surfaces of neutron stars as they spin, ultimately confronting the predictions of nuclear physics theory. Animation Credits: NASA’s Goddard Space Flight Center.

Technology advances in the past half-century allowed scientists to study these compact stellar objects from space using different wavelengths of light, especially those much more energetic than the radio waves received by the Cambridge telescope. Several current NASA missions continue to study these natural beacons.

The Neutron star Interior Composition Explorer, or NICER, is the first NASA mission dedicated to studying pulsars. In a nod to the anniversary of Bell’s discovery, NICER observed the famous first pulsar, known today as PSR B1919+21.

NICER launched to the International Space Station in early June and started science operations last month. Its X-ray observations – the part of the electromagnetic spectrum in which these stars radiate both from their million-degree solid surfaces and from their strong magnetic fields – will reveal how nature’s fundamental forces behave within the cores of these objects, an environment that doesn’t exist and can’t be reproduced anywhere else. "What's inside a pulsar?" is one of many long-standing astrophysics questions about these ultra-dense, fast-spinning, powerfully magnetic objects.

The “stuff” of pulsars is a collection of particles familiar to scientists from over a century of laboratory studies on Earth – neutrons, protons, electrons, and perhaps even their own constituents, called quarks. However, under such extreme conditions of pressure and density, their behavior and interactions aren’t well understood. New, precise measurements, especially of the sizes and masses of pulsars are needed to pin down theories.

“Many nuclear-physics models have been developed to explain how the make-up of neutron stars, based on available data and the constraints they provide,” said Goddard’s Keith Gendreau, the principal investigator for NICER. “NICER’s sensitivity, X-ray energy resolution and time resolution will improve these by more precisely measuring their radii, to an order of magnitude improvement over the state of the art today.”

Animation above: NICER is currently installed on the International Space Station. This turntable animation of the payload calls out the locations of NICER’s star tracker camera, electronics, space station attachment mechanism, 56 sunshields, pointing actuators and stow/deploy actuator. Animation Credits: NASA’s Goddard Space Flight Center.

The mission will also pave the way for future space exploration by helping to develop a Global Positioning System-like capability for the galaxy. The embedded Station Explorer for X-ray Timing and Navigation Technology, or SEXTANT, demonstration will use NICER’s X-ray observations of pulsar signals to determine NICER's exact position in orbit.

“You can time the pulsations of pulsars distributed in many directions around a spacecraft to figure out where the vehicle is and navigate it anywhere,” said Arzoumanian, who is also the NICER science lead. “That’s exactly how the GPS system on Earth works, with precise clocks flown on satellites in orbit.”

Scientists have tested this method using computer and lab simulations. SEXTANT will demonstrate pulsar-based navigation for the first time in space.

NICER-SEXTANT is the first astrophysics mission dedicated to studying pulsars, 50 years after their discovery. “I think it is going to yield many more scientific discoveries than we can anticipate now,” said Gendreau.

NICER-SEXTANT is a two-in-one mission. NICER is an Astrophysics Mission of Opportunity within NASA's Explorer program, which provides frequent flight opportunities for world-class scientific investigations from space utilizing innovative, streamlined, and efficient management approaches within the heliophysics and astrophysics science areas. NASA's Space Technology Mission Directorate supports the SEXTANT component of the mission, demonstrating pulsar-based spacecraft navigation.

NICER (Neutron star Interior Composition ExploreR): http://www.nasa.gov/nicer

Read about five famous pulsars from the past 50 years: https://nasa.tumblr.com/post/163637443034/five-famous-pulsars-from-the-past-50-years

Animations (mentioned), Image (mentioned), Text, Credits: NASA/Karl Hille/Goddard Space Flight Center, by Clare Skelly.

Greetings, Orbiter.ch

Gravity waves detected in Sun’s interior reveal rapidly rotating core

NASA & ESA - SOHO Mission patch.

1 August 2017

Scientists using the ESA/NASA SOHO solar observatory have found long-sought gravity modes of seismic vibration that imply the Sun’s core is rotating four times faster than its surface.

Just as seismology reveals Earth’s interior structure by the way in which waves generated by earthquakes travel through it, solar physicists use ‘helioseismology’ to probe the solar interior by studying sound waves reverberating through it. On Earth, it is usually one event that is responsible for generating the seismic waves at a given time, but the Sun is continuously ‘ringing’ owing to the convective motions inside the giant gaseous body.

Solar interior

Higher frequency waves, known as pressure waves (or p-waves), are easily detected as surface oscillations owing to sound waves rumbling through the upper layers of the Sun. They pass very quickly through deeper layers and are therefore not sensitive to the Sun’s core rotation.

Conversely, lower frequency gravity waves (g-waves) that represent oscillations of the deep solar interior have no clear signature at the surface, and thus present a challenge to detect directly.

In contrast to p-waves, for which pressure is the restoring force, buoyancy (gravity) acts as the restoring force of the gravity waves.

“The solar oscillations studied so far are all sound waves, but there should also be gravity waves in the Sun, with up-and-down, as well as horizontal motions like waves in the sea,” says Eric Fossat, lead author of the paper describing the result, published in Astronomy & Astrophysics.

“We’ve been searching for these elusive g-waves in our Sun for over 40 years, and although earlier attempts have hinted at detections, none were definitive. Finally, we have discovered how to unambiguously extract their signature.”

Eric and his colleagues used 16.5 years of data collected by SOHO’s dedicated ‘Global Oscillations at Low Frequencies’ (GOLF) instrument. By applying various analytical and statistical techniques, a regular imprint of the g-modes on the p-modes was revealed.

SOHO

In particular, they looked at a p-mode parameter that measures how long it takes for an acoustic wave to travel through the Sun and back to the surface again, which is known to be 4 hours 7 minutes. A series of modulations was detected in this p-mode parameter that could be interpreted as being due to the g-waves shaking the structure of the core.

The signature of the imprinted g-waves suggests the core is rotating once every week, nearly four times faster than the observed surface and intermediate layers, which vary from 25 days at the equator to 35 days at the poles.

“G-modes have been detected in other stars, and now thanks to SOHO we have finally found convincing proof of them in our own star,” adds Eric. “It is really special to see into the core of our own Sun to get a first indirect measurement of its rotation speed. But, even though this decades long search is over, a new window of solar physics now begins.”

The rapid rotation has various implications, for example: is there any evidence for a shear zone between the differently rotating layers? What do the periods of the g-waves tell us about the chemical composition of the core? What implication does this have on stellar evolution and the thermonuclear processes in the core?

“Although the result raises many new questions, making an unambiguous detection of gravity waves in the solar core was the key aim of GOLF. It is certainly the biggest result of SOHO in the last decade, and one of SOHO’s all-time top discoveries,” says Bernhard Fleck, ESA’s SOHO project scientist.

ESA’s upcoming solar mission, Solar Orbiter will also ‘look’ into the solar interior but its main focus is to provide detailed insights into the Sun’s polar regions, and solar activity. Meanwhile ESA’s future planet-hunting mission, Plato, will investigate seismic activity in stars in the exoplanet systems it discovers, adding to our knowledge of relevant processes in Sun-like stars.

Notes for editors:

“Asymptotic g modes: Evidence for a rapid rotation of the solar core”, by E. Fossat et al is published in Astronomy & Astrophysics: https://doi.org/10.1051/0004-6361/201730460

Related links:

ESA's SOHO home page: http://sohowww.estec.esa.nl/

The Sun now: http://www.esa.int/Our_Activities/Space_Science/The_Sun_now

SOHO in depth: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=14

Solar Orbiter: http://sci.esa.int/solar-orbiter/

Plato: http://sci.esa.int/plato/

Images, Text, Credits: ESA/Markus Bauer/Bernhard Fleck/Laboratoire Lagrange Université Côte d’Azur/Observatoire de la Côte d’Azur/Eric Fossat/SOHO (ESA & NASA)/ATG medialab.

Best regards, Orbiter.ch

NASA’s Voyager Spacecraft Still Reaching for the Stars After 40 Years

NASA - Voyager 1 & 2 Mission patch.

August 1, 2017

Humanity’s farthest and longest-lived spacecraft, Voyager 1 and 2, achieve 40 years of operation and exploration this August and September. Despite their vast distance, they continue to communicate with NASA daily, still probing the final frontier.

Their story has not only impacted generations of current and future scientists and engineers, but also Earth’s culture, including film, art and music. Each spacecraft carries a Golden Record of Earth sounds, pictures and messages. Since the spacecraft could last billions of years, these circular time capsules could one day be the only traces of human civilization.

“I believe that few missions can ever match the achievements of the Voyager spacecraft during their four decades of exploration,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate (SMD) at NASA Headquarters. “They have educated us to the unknown wonders of the universe and truly inspired humanity to continue to explore our solar system and beyond.”

Image above: An artist concept depicting one of the twin Voyager spacecraft. Humanity’s farthest and longest-lived spacecraft are celebrating 40 years in August and September 2017. Image Credit: NASA.

The Voyagers have set numerous records in their unparalleled journeys. In 2012, Voyager 1, which launched on Sept. 5, 1977, became the only spacecraft to have entered interstellar space. Voyager 2, launched on Aug. 20, 1977, is the only spacecraft to have flown by all four outer planets – Jupiter, Saturn, Uranus and Neptune. Their numerous planetary encounters include discovering the first active volcanoes beyond Earth, on Jupiter’s moon Io; hints of a subsurface ocean on Jupiter’s moon Europa; the most Earth-like atmosphere in the solar system, on Saturn’s moon Titan; the jumbled-up, icy moon Miranda at Uranus; and icy-cold geysers on Neptune's moon Triton.

Though the spacecraft have left the planets far behind – and neither will come remotely close to another star for 40,000 years – the two probes still send back observations about conditions where our Sun's influence diminishes and interstellar space begins.

Voyager 1, now almost 13 billion miles from Earth, travels through interstellar space northward out of the plane of the planets. The probe has informed researchers that cosmic rays, atomic nuclei accelerated to nearly the speed of light, are as much as four times more abundant in interstellar space than in the vicinity of Earth. This means the heliosphere, the bubble-like volume containing our solar system's planets and solar wind, effectively acts as a radiation shield for the planets. Voyager 1 also hinted that the magnetic field of the local interstellar medium is wrapped around the heliosphere.

Voyager 2, now almost 11 billion miles from Earth, travels south and is expected to enter interstellar space in the next few years. The different locations of the two Voyagers allow scientists to compare right now two regions of space where the heliosphere interacts with the surrounding interstellar medium using instruments that measure charged particles, magnetic fields, low-frequency radio waves and solar wind plasma. Once Voyager 2 crosses into the interstellar medium, they will also be able to sample the medium from two different locations simultaneously.

"None of us knew, when we launched 40 years ago, that anything would still be working, and continuing on this pioneering journey," said Ed Stone, Voyager project scientist based at Caltech in Pasadena, California. "The most exciting thing they find in the next five years is likely to be something that we didn't know was out there to be discovered."

The twin Voyagers have been cosmic overachievers, thanks to the foresight of mission designers. By preparing for the radiation environment at Jupiter, the harshest of all planets in our solar system, the spacecraft were well equipped for their subsequent journeys. Both Voyagers are equipped with long-lasting power supplies, as well as redundant systems that allow the spacecraft to switch to backup systems autonomously when necessary. Each Voyager carries three radioisotope thermoelectric generators, devices that use the heat energy generated from the decay of plutonium-238 – only half of it will be gone after 88 years.

Space is almost empty, so the Voyagers are not at a significant level of risk of bombardment by large objects. However, Voyager 1's interstellar space environment is not a complete void. It’s filled with clouds of dilute material remaining from stars that exploded as supernovae millions of years ago. This material doesn’t pose a danger to the spacecraft, but is a key part of the environment that the Voyager mission is helping scientists study and characterize.

Because the Voyagers' power decreases by four watts per year, engineers are learning how to operate the spacecraft under ever-tighter power constraints. And to maximize the Voyagers' lifespans, they also have to consult documents written decade’s earlier describing commands and software, in addition to the expertise of former Voyager engineers.

"The technology is many generations old, and it takes someone with 1970s design experience to understand how the spacecraft operate and what updates can be made to permit them to continue operating today and into the future," said Suzanne Dodd, Voyager project manager based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

Team members estimate they will have to turn off the last science instrument by 2030. However, even after the spacecraft go silent, they’ll continue on their trajectories at their present speed of more than 30,000 mph (48,280 kilometers per hour), completing an orbit within the Milky Way every 225 million years.

The Voyager spacecraft were built by JPL, which continues to operate both. The Voyager missions are part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of SMD.

For more information about the Voyager spacecraft, visit: https://www.nasa.gov/voyager and https://voyager.jpl.nasa.gov

Voyager Golden Record: https://www.nasa.gov/content/mementos-of-earth

Image (mentioned), Text, Credits: NASA/Dwayne Brown/Laurie Cantillo/JPL/Elizabeth Landau/Jia-Rui Cook.

Greetings, Orbiter.ch

Auroras Over Saturn Seen by Cassini Spacecraft

NASA Cassini Mission to Saturn patch.

July 31, 2017

Auroras Over Saturn Seen by Cassini Spacecraft

NASA's Cassini spacecraft gazed toward high southern latitudes near Saturn's south pole to observe ghostly curtains of dancing light -- Saturn's southern auroras, or southern lights. These natural light displays at the planet's poles are created by charged particles raining down into the upper atmosphere, making gases there glow. The dark area at the top of this scene is Saturn's night side. The auroras rotate from left to right, curving around the planet as Saturn rotates over about 70 minutes, compressed here into a movie sequence of about five seconds. For more information about this clip, visit https://go.nasa.gov/2uFOSPw. Video Credits: NASA/JPL-Caltech/Space Science Institute.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

Image above: Auroras Over Saturn Seen by Cassini Spacecraft. Image Credits: NASA/JPL-Caltech/Space Science Institute.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org and ESA's website: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Image (mentioned), Video (mentioned), Text, Credits: NASA/JPL.

Greetings, Orbiter.ch

An Earth-like Atmosphere May Not Survive Proxima b’s Orbit

NASA - Chandra X-ray Observatory patch.

July 31, 2017

Proxima b, an Earth-size planet right outside our solar system in the habitable zone of its star, may not be able to keep a grip on its atmosphere, leaving the surface exposed to harmful stellar radiation and reducing its potential for habitability.

At only four light-years away, Proxima b is our closest known extra-solar neighbor. However, due to the fact that it hasn't been seen crossing in front of its host star, the exoplanet eludes the usual method for learning about its atmosphere. Instead, scientists must rely on models to understand whether the exoplanet is habitable.

One such computer model considered what would happen if Earth orbited Proxima Centauri, our nearest stellar neighbor and Proxima b’s host star, at the same orbit as Proxima b. The NASA study, published on July 24, 2017, in The Astrophysical Journal Letters, suggests Earth’s atmosphere wouldn’t survive in close proximity to the violent red dwarf.

“We decided to take the only habitable planet we know of so far — Earth — and put it where Proxima b is,” said Katherine Garcia-Sage, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study. The research was supported by NASA’s NExSS coalition — leading the search for life on planets beyond our solar system — and the NASA Astrobiology Institute.

Image above: At its orbit, the exoplanet Proxima b likely couldn’t sustain an Earth-like atmosphere. Image Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith.

Just because Proxima b’s orbit is in the habitable zone, which is the distance from its host star where water could pool on a planet’s surface, doesn’t mean it’s habitable. It doesn’t take into account, for example, whether water actually exists on the planet, or whether an atmosphere could survive at that orbit. Atmospheres are also essential for life as we know it: Having the right atmosphere allows for climate regulation, the maintenance of a water-friendly surface pressure, shielding from hazardous space weather, and the housing of life’s chemical building blocks.

Garcia-Sage and her colleagues’ computer model used Earth’s atmosphere, magnetic field and gravity as proxies for Proxima b’s. They also calculated how much radiation Proxima Centauri produces on average, based on observations from NASA’s Chandra X-ray Observatory.

With these data, their model simulates how the host star’s intense radiation and frequent flaring affect the exoplanet’s atmosphere.

“The question is, how much of the atmosphere is lost, and how quickly does that process occur?” said Ofer Cohen, a space scientist at the University of Massachusetts, Lowell and co-author of the study. “If we estimate that time, we can calculate how long it takes the atmosphere to completely escape — and compare that to the planet’s lifetime.”

An active red dwarf star like Proxima Centauri strips away atmosphere when high-energy extreme ultraviolet radiation ionizes atmospheric gases, knocking off electrons and producing a swath of electrically charged particles. In this process, the newly formed electrons gain enough energy that they can readily escape the planet’s gravity and race out of the atmosphere.

Opposite charges attract, so as more negatively charged electrons leave the atmosphere, they create a powerful charge separation that pulls positively charged ions along with them, out into space.

In Proxima Centauri’s habitable zone, Proxima b encounters bouts of extreme ultraviolet radiation hundreds of times greater than Earth does from the sun. That radiation generates enough energy to strip away not just the lightest molecules — hydrogen — but also, over time, heavier elements such as oxygen and nitrogen.

The model shows Proxima Centauri’s powerful radiation drains the Earth-like atmosphere as much as 10,000 times faster than what happens at Earth.

Image above: This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the solar system. Image Credits: ESO/M. Kornmesser.

“This was a simple calculation based on average activity from the host star,” Garcia-Sage said. “It doesn’t consider variations like extreme heating in the star’s atmosphere or violent stellar disturbances to the exoplanet’s magnetic field — things we’d expect provide even more ionizing radiation and atmospheric escape.”

To understand how the process can vary, the scientists looked at two other factors that exacerbate atmospheric loss. First, they considered the temperature of the neutral atmosphere, called the thermosphere. They found as the thermosphere heats with more stellar radiation, atmospheric escape increases.

The scientists also considered the size of the region over which atmospheric escape happens, called the polar cap. Planets are most sensitive to magnetic effects at their magnetic poles. When magnetic field lines at the poles are closed, the polar cap is limited and charged particles remain trapped near the planet. On the other hand, greater escape occurs when magnetic field lines are open, providing a one-way route to space.

“This study looks at an under-appreciated aspect of habitability, which is atmospheric loss in the context of stellar physics,” said Shawn Domagal-Goldman, a Goddard space scientist not involved in the study. “Planets have lots of different interacting systems, and it’s important to make sure we include these interactions in our models.”

The scientists show that with the highest thermosphere temperatures and a completely open magnetic field, Proxima b could lose an amount equal to the entirety of Earth’s atmosphere in 100 million years — that’s just a fraction of Proxima b’s 4 billion years thus far. When the scientists assumed the lowest temperatures and a closed magnetic field, that much mass escapes over 2 billion years.

Chandra X-ray Observatory. Animation Credits: NASA/CXC

“Things can get interesting if an exoplanet holds on to its atmosphere, but Proxima b’s atmospheric loss rates here are so high that habitability is implausible,” said Jeremy Drake, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics and co-author of the study. “This questions the habitability of planets around such red dwarfs in general.”

Red dwarfs like Proxima Centauri or the TRAPPIST-1 star are often the target of exoplanet hunts, because they are the coolest, smallest and most common stars in the galaxy. Because they are cooler and dimmer, planets have to maintain tight orbits for liquid water to be present.

But unless the atmospheric loss is counteracted by some other process — such as a massive amount of volcanic activity or comet bombardment — this close proximity, scientists are finding more often, is not promising for an atmosphere’s survival or sustainability.

For more information, go to: https://exoplanets.nasa.gov

Related articles:

Flares May Threaten Planet Habitability Near Red Dwarfs: http://orbiterchspacenews.blogspot.ch/2017/06/flares-may-threaten-planet-habitability.html

NASA’s NexSS Coalition to Lead Search for Life on Distant Worlds: https://www.nasa.gov/feature/nasa-s-nexss-coalition-to-lead-search-for-life-on-distant-worlds

Related links:

Proxima b: http://orbiterchspacenews.blogspot.ch/2016/08/planet-found-in-habitable-zone-around.html

TRAPPIST-1 star: https://www.nasa.gov/press-release/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around

The Astrophysical Journal Letters: https://doi.org/10.3847/2041-8213/aa7eca

NASA’s Chandra X-ray Observatory: https://www.nasa.gov/mission_pages/chandra/astronomy/index.html

Images (mentioned), Animation (mentioned), Text, Credits: NASA/Rob Garner/Goddard Space Flight Center, by Lina Tran.

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