Mars’ atmospheric history

Mars’ atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar

Most of Mars’ atmosphere has been lost

Mars has a thin atmosphere composed mainly of carbon dioxide. Evidence on the planet’s surface indicates that Mars was once warmer and wetter, suggesting a thicker atmosphere in the past. Jakosky et al. measured the abundances of argon isotopes at different heights in the atmosphere. Because lighter isotopes are more easily ejected than heavier ones, about 66% of Mars’ atmosphere has been lost into space since it formed. Understanding the history of Mars’ atmosphere will help explain how and why its climate changed, informing the study of similar processes on Earth.

Abstract

The history of Mars’ atmosphere is important for understanding the geological evolution and potential habitability of the planet. We determine the amount of gas lost to space through time using measurements of the upper-atmospheric structure made by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. We derive the structure of 38Ar/36Ar between the homopause and exobase altitudes. Fractionation of argon occurs as a result of loss of gas to space by pickup-ion sputtering, which preferentially removes the lighter atom. The measurements require that 66% of the atmospheric argon has been lost to space. Thus, a large fraction of Mars’ atmospheric gas has been lost to space, contributing to the transition in climate from an early, warm, wet environment to today’s cold, dry atmosphere.

 

An ArduSiPM Cosmic Ray detektor

An educational distributed Cosmic Ray detector network based on ArduSiPM

ABSTRACT: The advent of microcontrollers with enough CPU power and with analog and digital peripherals makes possible to design a complete particle detector with relative acquisition system around one microcontroller chip. The existence of a world wide data infrastructure as internet allows for devising a distributed network of cheap detectors capable to elaborate and send data or respond to settings commands. The internet infrastructure enables to distribute the absolute time (with precision of few milliseconds), to the simple devices far apart, with few milliseconds precision, from a few meters to thousands of kilometres. So it is possible to create a crowdsourcing experiment of citizen science that use small scintillation-based particle detectors to monitor the high energetic cosmic ray and the radiation environment.

 

Frequent flaring in TRAPPIST-1

Frequent flaring in the TRAPPIST-1 system – unsuited for life?

ABSTRACT: We analyze short cadence K2 light curve of the TRAPPIST-1 system. Fourier analysis of the data suggests Prot = 3.295±0.003 days. The light curve shows several flares, of which we analyzed 42 events, these have integrated flare energies of 1.26×1030-1.24×1033 ergs. Approximately 12% of the flares were complex, multi-peaked eruptions. The flaring and the possible rotational modulation shows no obvious correlation. The flaring activity of TRAPPIST-1 probably continuously alters the atmospheres of the orbiting exoplanets, making these less favorable for hosting life.

 

Measuring R and M of Planet Nine

Measuring the radius and mass of Planet Nine

ABSTRACT: Batygin and Brown (2016) have suggested the existence of a new Solar System planet supposed to be responsible for the perturbation of eccentric orbits of small outer bodies. The main challenge is now to detect and characterize this putative body. Here we investigate the principles of the determination of its physical parameters, mainly its mass and radius. For that purpose we concentrate on two methods, stellar occultations and gravitational microlensing effects (amplification, deflection and time delay). We estimate the main characteristics of a possible occultation or gravitational effects: flux variation of a background star, duration and probability of occurence. We investigate also additional benefits of direct imaging and of an occultation.

 

NASA Selects CubeSat to study Venus

Venus created from Magellian data.

NASA Selects CubeSat, SmallSat Mission Concept Studies

NASA has selected 10 studies under the Planetary Science Deep Space SmallSat Studies (PSDS3) program to develop mission concepts using small satellites to investigate Venus, Earth’s moon, asteroids, Mars and the outer planets.

For these studies, small satellites are defined as less than 180 kilograms in mass (about 400 pounds). CubeSats are built to standard specifications of 1 unit (U), which is equal to about 4x4x4 inches (10x10x10 centimeters). They often are launched into orbit as auxiliary payloads, significantly reducing costs.

“These small but mighty satellites have the potential to enable transformational science,” said Jim Green, director of the Planetary Science Division at NASA Headquarters in Washington. “They will provide valuable information to assist in planning future Announcements of Opportunity, and to guide NASA’s development of small spacecraft technologies for deep space science investigation.”

NASA’s Science Mission Directorate is developing a small satellite strategy, with the goal of identifying high-priority science objectives in each discipline that can be addressed with CubeSats and SmallSats, managed for appropriate cost and risk. This multi-disciplinary approach will leverage and partner with the growing commercial sector to collaboratively drive instrument and sensor innovation.

The PSDS3 awardees were recognized this week at the 48th Lunar and Planetary Society Conference in The Woodlands, Texas. The total value of the awards is $3.6 million.

Venus

Christophe Sotin, NASA’s Jet Propulsion Laboratory, Pasadena, California: Cupid’s Arrow, a 66-pound (30-kilogram) probe to measure noble gases and their isotopes to investigate the geological evolution of Venus and why Venus and Earth have evolved so differently.

Valeria Cottini, University of Maryland, College Park: CubeSat UV Experiment (CUVE), a 12-unit CubeSat orbiter to measure ultraviolet absorption and nightglow emissions to understand Venus’ atmospheric dynamics.

 

Juno completes fifth flyby

Juno Spacecraft Completes Fifth Jupiter Flyby

Updated March 27, 2017 at 1:45 p.m. PDT

NASA’s Juno mission accomplished a close flyby of Jupiter on Monday, March 27, successfully completing its fourth science orbit.

All of Juno’s science instruments and the spacecraft’s JunoCam were operating during the flyby, collecting data that is now being returned to Earth. Juno’s next close flyby of Jupiter will occur on May 19, 2017.

The Juno science team continues to analyze returns from previous flybys. Scientists have discovered that Jupiter’s magnetic fields are more complicated than originally thought, and that the belts and zones that give the planet’s cloud tops their distinctive look extend deep into the its interior. Observations of the energetic particles that create the incandescent auroras suggest a complicated current system involving charged material lofted from volcanoes on Jupiter’s moon Io.

Peer-reviewed papers with more in-depth science results from Juno’s first flybys are expected to be published within the next few months.

 

The EnVision Venus orbiter

EnVision: understanding why our most Earth-like neighbour is so different

ABSTRACT: This document is the EnVision Venus orbiter proposal, submitted in October 2016 in response to ESA’s M5 call for Medium-size missions for its Science Programme, for launch in 2029.
Why are the terrestrial planets so different? Venus should be the most Earth-like of all our planetary neighbours: its size, bulk composition and distance from the Sun are very similar to those of Earth. Its original atmosphere was probably similar to that of early Earth, with abundant water that would have been liquid under the young sun’s fainter output. Even today, with its global cloud cover, the surface of Venus receives less solar energy than does Earth, so why did a moderate climate ensue here but a catastrophic runaway greenhouse on Venus? How and why did it all go wrong for Venus? What lessons can be learned about the life story of terrestrial planets in general, in this era of discovery of Earth-like exoplanets? Were the radically different evolutionary paths of Earth and Venus driven solely by distance from the Sun, or do internal dynamics, geological activity, volcanic outgassing and weathering also play an important part?
Following the primarily atmospheric focus of Venus Express, we propose a new Venus orbiter named EnVision, to focus on Venus’ geology and geochemical cycles, seeking evidence for present and past activity. The payload comprises a state-of-the-art S-band radar which will be able to return imagery at spatial resolutions of 1 – 30 m, and capable of measuring cm-scale deformation; this is complemented by subsurface radar, IR and UV spectrometers to map volcanic gases, and by geodetic investigations.

 

No kinematic backreaction

There is no kinematic backreaction

ABSTRACT: In the conventional framework for cosmological dynamics the scale factor a(t) is assumed to obey the `background’ Friedmann equation for a perfectly homogeneous universe while particles move according to equations of motions driven by the gravity sourced by the density fluctuations. It has been suggested that the emergence of structure modifies the evolution of a(t) via `kinematic’ backreaction and that this may avoid the need for dark energy. Here we show that the conventional equations are exact in Newtonian gravity — which should accurately describe the low-z universe — and there is no approximation in the use of the homogeneous universe equation for a(t). We conclude that there is no backreaction of structure on a(t) and that the need for dark energy cannot be avoided in this way.

Comment on: “There is no kinematic backreaction” by N. Kaiser

ABSTRACT: We clarify that a result recently stated by Kaiser [arXiv:1703.08809v1] is contained in a theorem of Buchert and Ehlers that is widely known for its main result: that there is no global kinematical backreaction in Newtonian cosmology. Kaiser cites this paper but incompletely restates its content. He makes further claims, which cannot be proven beyond the limited context of Newtonian cosmology in which the theorem applies.

 

Earth-mass Planet around Brown Dwarf

An Earth-mass Planet in a 1-AU Orbit around a Brown Dwarf

ABSTRACT: We combine Spitzer and ground-based KMTNet microlensing observations to identify and precisely measure an Earth-mass (1.32+0.41-0.28 M) planet OGLE-2016-BLG-1195Lb at 1.11+0.13-0.10 AU orbiting a 0.072+0.014-0.010 M ultracool dwarf, likely a brown dwarf. This is the lowest-mass microlensing planet to date. At 4.20+0.29-0.34 kpc, it is the third consecutive case among the Spitzer “Galactic distribution” planets toward the Galactic bulge that lies in the Galactic disk as opposed to the bulge itself, hinting at a skewed distribution of planets. Together with previous microlensing discoveries, the seven Earth-size planets orbiting the ultracool dwarf TRAPPIST-1, and the detection of disks around young brown dwarfs, OGLE-2016-BLG-1195Lb suggests that such planets might be common around ultracool dwarfs. It therefore sheds light on the formation of both brown dwarfs and planetary systems at the limit of low-mass protoplanetary disks.

 

Why care about TRAPPIST-1?

Comments by Luca Maltagliati.

Exoplanets: Why should we care about TRAPPIST-1?

The discovery of a system of six (possibly seven) terrestrial planets around the TRAPPIST-1 star, announced in a paper by Michaël Gillon and collaborators attracted a great deal of attention from researchers as well as the general public. Reactions ranged from the enthusiastic — already hypothesizing a string of inhabited planets — to those who felt that it didn’t add anything substantial to our current knowledge of exoplanets and was ultimately not worth the hype. The cover of the Nature issue hosting the paper (pictured), made by Robert Hurt, a visualization scientist at Caltech, is a fine piece of artwork, but it also helps us in assessing the actual relevance of the TRAPPIST-1 system.

Firstly, the cover shows a very packed system. This corresponds to reality: all seven planets would fit well within the orbit of Mercury. In fact, the closest analogue of the TRAPPIST-1 system is not our Solar System, but Jupiter and its Galilean moons. TRAPPIST-1 itself is only 1.1 times bigger than Jupiter, and the distance between its innermost and outermost planets, expressed in orbital period, is almost coincident with that between Io and Callisto.

Then, at least six of the planets have radii and masses — and, consequently, densities — close to those of the Earth. They can thus be called ‘terrestrial’ without any qualms about terminology. In addition, even if the whole system is much less massive than our Solar System, the ratio of the total planetary mass to the mass of the star is comparable (1/4,000 for TRAPPIST-1 versus 1/5,500 for us). This is puzzling as, according to our current models of planetary formation, the total amount of matter in the system should play a role in the efficiency of planetary accretion.

The TRAPPIST-1 planets also form a quasi-resonant chain of orbits (where their orbital periods can be expressed as a ratio of two small numbers), again not dissimilar to what happens in the Jovian system between Io, Europa and Ganymede. This is the first system we’ve found with terrestrial planets tightly packed together and in resonance.

Their orbits are also all co-planar, as the image shows, and luckily for us this orbital plane passes through the line of sight between us and TRAPPIST-1: all these planets are ‘transiting’. This is much more than a simple technical detail, as it allows us to characterize all their atmospheres — an essential step to understand their climate and propensity for habitability.

Finally and maybe most importantly, these planets are distributed over all of the three zones related to different phases of water, as cleverly represented by the illustration. However, this information, linked to the concept of habitable or temperate zone and the possible presence of liquid water on the surface, must be taken with caution, since we do not yet know whether any of the TRAPPIST-1 planets have either an atmosphere or the albedo required for liquid water to survive.

In conclusion, the TRAPPIST-1 system will provide a planetary-scale laboratory to test and constrain all sorts of theories and models concerning planetary formation and evolution, atmospheres, interplanetary interaction and potential for habitability. So yes, we should definitely care about TRAPPIST-1, even if we won’t be able to establish a colony there anytime soon.