Category Archives: Planetary Science

Juno Discovers ‘Shallow Lightning’ on Jupiter (Astronomy / Planetary Science)

According to a new analysis of data collected by the Stellar Reference Unit instrument onboard NASA’s Juno spacecraft, an unexpected form of electrical discharge, ‘shallow lightning’ originates from Jovian clouds containing an ammonia-water solution.

Fig: This illustration uses data obtained by NASA’s Juno mission to depict high-altitude electrical storms on Jupiter. Juno’s Stellar Reference Unit camera detected unusual lightning flashes on Jupiter’s dark side during the spacecraft’s close flybys of the planet. Image credit: NASA / JPL-Caltech / SwRI / MSSS / Gerald Eichstädt.

Since NASA’s Voyager mission first saw Jovian lightning flashes in 1979, it has been thought that the planet’s lightning is similar to Earth’s, occurring only in thunderstorms where water exists in all its phases — ice, liquid, and gas.

At Jupiter this would place the storms around 45 to 65 km (28-40 miles) below the visible clouds, with temperatures that hover around 0 degrees Celsius (32 degrees Fahrenheit).

Voyager, and all other missions to the gas giant prior to Juno, saw lightning as bright spots on Jupiter’s cloud tops, suggesting that the flashes originated in deep water clouds.

But lightning flashes observed on Jupiter’s dark side by Juno’s Stellar Reference Unit tell a different story.

Ammonia is the key. While there is water and other chemical elements such as molecular hydrogen and helium in Jupiter’s clouds, ammonia is the antifreeze that keeps water in those upper atmospheric clouds from freezing entirely.

The collision of the falling droplets of mixed ammonia and water with suspended water-ice particles constitutes a way to separate charge and produce cloud electrification — resulting in lightning storms in the upper atmosphere.

The spatial resolution of some cameras allowed investigators to confirm 22 flashes with HWHM greater than 42 kilometres, and to estimate one with an HWHM of 37 to 45 kilometres. These flashes, with optical energies comparable to terrestrial ‘superbolts’—of (0.02–1.6) × 10^10 joules—have been interpreted as tracers of moist convection originating near the 5-bar level of Jupiter’s atmosphere (assuming photon scattering from points beneath the clouds).

Previous observations of lightning have been limited by camera sensitivity, distance from Jupiter and long exposures (about 680 milliseconds to 85 seconds), meaning that some measurements were probably superimposed flashes reported as one.

Authors reported optical observations of lightning flashes by the Juno spacecraft with energies of approximately 10^5–10^8 joules, flash durations as short as 5.4 milliseconds and inter-flash separations of tens of milliseconds, with typical terrestrial energies.

The flash rate is about 6.1 × 10^−2 flashes per square kilometre per year, more than an order of magnitude greater than hither to seen. Several flashes are of such small spatial extent that they must originate above the 2-bar level, where there is no liquid water. This implies that multiple mechanisms for generating lightning on Jupiter need to be considered for a full understanding of the planet’s atmospheric convection and composition.


References: (1) H.N. Becker et al. 2020. Small lightning flashes from shallow electrical storms on Jupiter. Nature 584, 55-58; doi: 10.1038/s41586-020-2532-1 link: https://www.nature.com/articles/s41586-020-2532-1

Ice Sheets Covered Southern Highlands of Early Mars (Astronomy / Planetary Science)

The southern highlands of Mars are dissected by hundreds of ancient valley networks (3.9-3.5 billion years old), which are evidence that water once sculpted the Martian surface. According to new research, these valley networks were carved by water melting beneath glacial ice, not by free-flowing rivers as previously thought.

Fig: A view of Mars showing the planet’s northern polar ice cap. Image credit: ISRO / ISSDC / Emily Lakdawalla.

The similarity between many Martian valleys and the subglacial channels on Devon Island in the Canadian Arctic motivated Dr. Grau Galofre and colleagues to conduct this new study.

Fig: A glacial valley network on Mars. Image credit: Grau Galofre et al.

In the study, the scientists analyzed 10,276 Martian valley segments, using a novel algorithm to infer their underlying erosion processes.

They used data from the Mars Orbiter Laser Altimeter (MOLA) instrument on NASA’s Mars Global Surveyor spacecraft and the High Resolution Stereo Camera (HRSC) on ESA’s Mars Express orbiter.

These results are the first evidence for extensive subglacial erosion driven by channelized meltwater drainage beneath an ancient ice sheet on Mars. The findings demonstrated that only a fraction of valley networks match patterns typical of surface water erosion, which is in marked contrast to the conventional view.

Using the geomorphology of the Martian surface to rigorously reconstruct the character and evolution of the planet in a statistically meaningful way is, frankly, revolutionary.

Fig: Distribution of Martian valley networks (purple) and those analyzed (white) by Grau Galofre et al. Image credit: Grau Galofre et al, doi: 10.1038/s41561-020-0618-x.

The team’s theory also helps explain how the Martian valleys would have formed 3.8 billion years ago on a planet that is further away from the Sun than Earth, during a time when the Sun was less intense.

Climate modeling predicts that Mars’ ancient climate was much cooler during the time of valley network formation. They tried to put everything together and came up with a hypothesis that hadn’t really been considered: that channels and valleys networks can form under ice sheets, as part of the drainage system that forms naturally under an ice sheet when there’s water accumulated at the base.

These environments would also support better survival conditions for possible ancient life on Mars.

A sheet of ice would lend more protection and stability of underlying water, as well as providing shelter from solar radiation in the absence of a magnetic field — something Mars once had, but which disappeared billions of years ago.


References: Anna Grau Galofre, A. Mark Jellinek & Gordon R. Osinski, “Valley formation on early Mars by subglacial and fluvial erosion”, Nature Geoscience, published online August 3, 2020; doi: 10.1038/s41561-020-0618-x ; Link: https://www.nature.com/articles/s41561-020-0618-x

Perseverance Launches to Hunt for Signs of Ancient Martian Life (Planetary Science / Astronomy)

NASA’s Mars 2020 Perseverance rover and Ingenuity helicopter launched on a United Launch Alliance Atlas V 541 rocket from Space Launch Complex 41 at Cape Canaveral Air Force Station at 7:50 a.m. EDT on July 30, 2020.

The Perseverance rover mission will address high-priority science goals for Mars exploration.

Developed under NASA’s Mars Exploration Program, it will seek signs of past microbial life and characterize the planet’s climate and geology.

It will also collect samples of Martian rocks and dust for a future Mars Sample Return mission to Earth, while paving the way for human exploration of the Red Planet.

Perseverance will land in Jezero Crater on Mars on February 18, 2021.

Home to a lake billions of years ago, Jezero isn’t a typical Mars crater.

The car-sized Perseverance is also the largest, heaviest robotic Mars rover NASA has built.

The rover is about 3 m (10 feet) long not including the robotic arm, 2.7 m (9 feet) wide and 2.1 m (7 feet) tall. But at 1,025 kg (2,260 pounds), it weighs less than a compact car.

Its robotic arm is equipped with a rotating turret, which includes a rock drill, science instruments and a camera.

But while Perseverance’s arm is 2.1 m (7 feet) long, just like Curiosity’s, its turret weighs more — 45 kg (99 pounds) — because it carries larger instruments and a larger drill for coring. The drill will cut intact rock cores, and they’ll be placed in sample tubes via a complex storage system.

Perseverance also has a six-wheel, rocker-bogie design derived from all of NASA’s Mars rovers to date that helps to maintain a relatively constant weight on each of the rover’s wheels and minimizes tilt.

The wheels are slightly narrower and taller than Curiosity’s but are similarly machined out of a rigid, lightweight aluminum alloy.

Both Curiosity and Perseverance have wheels lined with grousers — raised treads that are specially designed for the Martian desert.

Fig: This artist’s concept depicts NASA’s Mars rover Perseverance on the surface of the Red Planet. Image credit: NASA / JPL-Caltech.

Perseverance is carrying seven different scientific instruments:

(i) Mastcam-Z is an advanced camera system with panoramic and stereoscopic imaging capability with the ability to zoom;

(ii) SuperCam is an instrument that can provide imaging, chemical composition analysis, and mineralogy at a distance;

(iii) Planetary Instrument for X-ray Lithochemistry (PIXL) is an X-ray fluorescence spectrometer and high-resolution imager, which will map the fine-scale elemental composition of Martian surface materials;

(iv) Scanning Habitable Environments with Raman & Luminescence for Organics and Chemicals (SHERLOC) is a spectrometer that will provide fine-scale imaging and uses an ultraviolet (UV) laser to map mineralogy and organic compounds;

(v) The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) is a technology demonstration that will produce oxygen from Martian atmospheric carbon dioxide;

(vi) Mars Environmental Dynamics Analyzer (MEDA) is a set of sensors that will provide measurements of temperature, wind speed and direction, pressure, relative humidity, and dust size and shape;

(vii) Radar Imager for Mars’ Subsurface Experiment (RIMFAX) is a ground-penetrating radar that will provide centimeter-scale resolution of the geologic structure of the subsurface.

Another special feature on Perseverance can be found on the aft crossbeam: a plate that contains three silicon chips stenciled with the names of approximately 10.9 million people from around the world who participated in the online ‘Send Your Name to Mars’ campaign from May to September 2019.

The fingernail-sized chips also contain the essays of 155 finalists in NASA’s ‘Name the Rover’ essay contest.

The chips share space on an anodized plate with a laser-etched graphic depicting Earth and Mars joined by the star that gives light to both and a message in Morse code in the Sun’s rays: ‘Explore as one.’

Perseverance is also bringing a twin-rotor, solar-powered helicopter named Ingenuity to test out aerial flight on another planet for the first time.

Perseverance is ferrying 23 cameras to the Red Planet — the most ever flown in the history of deep-space exploration. Two cameras are installed on the Ingenuity helicopter.

References: (1) https://www.nasa.gov/perseverance/overview/ (2) https://www.planetary.org/space-images/jezero-crater-mars (3) https://theuncoverreality.wordpress.com/2020/07/31/nasas-mars-2020-rover-will-have-23-cameras-astronomy-mission-science-and-technology/

Moon May Be 85 Million Years Younger than Previously Thought (Astronomy)

According to a new modeling study by M. Maurice & colleagues, Earth’s only natural satellite formed 4.425 billion years ago — around 85 million years later than previous estimates..

Fig: When the Moon formed into a sphere approximately 1,700 km in radius 4.425 billion years ago, its interior heated up considerably due to the energy released when it accreted. The rock melted and an ocean of magma, possibly more than 1,000 km deep, formed. Later, light rocks crystallized, which rose to the surface and formed a first crust on the Moon. This crust insulated the Moon from space, and the magma ocean beneath it cooled down slowly. Around 200 million years would pass before the Moon completely solidified. Image credit: NASA’s Goddard Space Flight Center.

According to the giant impact hypothesis, the Moon was created out of the debris left over from a catastrophic collision between the proto-Earth and a Mars-sized protoplanet called Theia.

This collision produced a lunar magma ocean and initiated the last event of core segregation on Earth. However, the timing of these events remains uncertain.

The scientists determined when the Moon was formed using a new, indirect method & they demonstrated that the lunar magma ocean quickly began to solidify and formed a crust of floating, lightweight crystals at the surface — its ‘interface’ with the cold space.

But under this insulating crust, which slowed down the further cooling and solidification of the magma ocean, the Moon remained molten for a long time.

Until now, scientists were unable to determine how long it took for the magma ocean to crystallize completely, which is why they could not conclude when the Moon originally formed.

To calculate the lifetime of the Moon’s magma ocean, the authors used a new computer model, which for the first time comprehensively considered the processes involved in the solidification of the magma.

& their results from the model showed that the Moon’s magma ocean was long-lived and took almost 200 million years to completely solidify into mantle rock. The time scale is much longer than calculated in previous studies. Older models gave a solidification period of only 35 million years.

To determine the age of the Moon, the team calculated how the composition of the magnesium- and iron-rich silicate minerals that formed during the solidification of the magma ocean changed over time.

The researchers discovered a drastic change in the composition of the remaining magma ocean as solidification progressed.

This finding is significant because it allowed them to link the formation of different types of rock on the Moon to a certain stage in the evolution of its magma ocean.

By comparing the measured composition of the Moon’s rocks with the predicted composition of the magma ocean from their model, they were able to trace the evolution of the ocean back to its starting point, the time at which the Moon was formed.

The results showed that the Moon was formed 4.425 billion years ago.

This age is in remarkable agreement with an age previously determined for the formation of Earth’s metallic core with the uranium-lead method, the point at which the formation of the Earth was completed.

References: M. Maurice, N. Tosi, S. Schwinger, D. Breuer and T. Kleine, “A long-lived magma ocean on a young Moon”, Science Advances 10 Jul 2020:
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