Space Sunday: Pluto’s names, Jupiter’s core

The 14 new surface feature names (in yellow) approved for Pluto by the International Astronomical Union on August 8th, 2019. The names in white were approved by the IAU in 2017. Credit: NASA / JHU/APL

On August 8th, 2019, the International Astronomical Union (IAU) approved the names for 14 more significant features on the surface of Pluto, imaged by the New Horizons space vehicle as it flew past the Pluto-Charon system in 2015.

The IAU claimed the authority to officially name or approve the name of planets, dwarf planets, moons, asteroids and planetary features in our solar system during its inaugural General Assembly, held in Rome in May 1922, 3 years after it had been formed by the founding nations of Belgium, Canada, France, Great Britain, Greece, Japan, and the United States, and by which point its membership had grown to 19 nations around the world (today membership stands at 82 nations).

As the sole authority, it means that any names given to things like planetary surface features  – such as “Mount Sharp” on the surface of Mars are entirely unofficial, hence why they are referred to in quotes in these Space Sunday articles. The IAU may determine names on things like surface features entirely by itself (as is the case with “Mount Sharp”, which is officially designated Aeolis Mons), or they may take recommendations from other organisations or groups.

In the case of the 14 names first assigned to features on Pluto by the IAU in 2017, the organisation ratified the suggestions made by the New Horizons mission team. Keeping with this “tradition”, the August 8th, 2019 announcement of the 14 “new” names for surface features first employed by the mission team.

The first 14 names to be approved by the IAU (2017) for features on Pluto include the Tombaugh Regio, named for Clyde Tombaugh, who first identified Pluto as a planetary body; the great frozen nitrogen lake of Sputnik Planitia, and the Hillary and Tenzing mountains, named for the two men formally recorded as the first to reach the summit of Mount Everest. Credit: NASA / JHU/APL

All 14 represent people and missions that contributed to the understanding of Pluto and the Kuiper Belt, as well as drawing on figures from mythology and aerospace exploration in general. They cover a range of surface features on Pluto images by the New Horizons vehicle as it dashed through the Pluto-Charon system that include entire regions of the planet and items such as mountain ranges, plains, valleys and craters. They comprise (in alphabetically order):

  • Alcyonia Lacus, possibly a frozen nitrogen lake, it is named for the “bottomless” lake in the vicinity of Lerna, Greece, and regarded as one of the entrances to the underworld in Greek mythology.
  • Elcano Montes, a mountain range named for Juan Sebastián Elcano (1476–1526), the Spanish explorer who in 1522 completed the first circumnavigation of the Earth (a voyage started in 1519 by Magellan).
  • Hunahpu Valles, a system of canyons named for after one of the Mayan Hero Twins who defeated the lords of the underworld in a ball game.
  • Khare crater honours planetary scientist Bishun Khare (1933–2013), who specialised in the chemistry of planetary atmospheres and who published several seminal papers on tholins, the organic molecules that probably account for the darkest and reddest regions on Pluto.
  • Kiladze crater is named for Rolan Il’ich Kiladze (1931–2010), who made pioneering early investigations the dynamics, astrometry and photometry of Pluto.
  • Lowell Regio, is a large region honouring Percival Lowell (1855–1916), founder of the Lowell Observatory and organiser of the search that eventually led Clyde Tombaugh to locate Pluto.
  • Mwindo Fossae, a network of long, narrow depressions named for the Mwindo Epic of the Nyanga people.
  • Piccard Mons, a mountain and suspected cryovolcano named for Swiss inventor and physicist and high altitude balloon pioneer, Auguste Piccard (1884–1962).
  • Pigafetta Montes, a mountain range honouring Antonio Pigafetta (c. 1491–c. 1531), the Italian scholar and explorer who chronicled the discoveries made during the first circumnavigation of the Earth, aboard Magellan’s ships.
  • Piri Rupes, a range of cliffs named for Piri Reis (also Ahmed Muhiddin Piri c. 1470–1553), an Ottoman navigator and cartographer known for his world map. He also drew some of the earliest existing maps of North and Central America.
  • Simonelli crater, name after astronomer Damon Simonelli (1959–2004), whose wide-ranging research included the formation history of Pluto.
  • Wright Mons, a mountain named for powered flight pioneers Orville and Wilbur Wright.
  • Vega Terra, a large land mass named after the Soviet Vega 1 and 2 missions, the first spacecraft to fly balloons on another planet (Venus) and to image the nucleus of a comet (1P/Halley).
  • Venera Terra, named for the Venera missions sent to Venus by the Soviet Union from 1961–1984; they included the first human-made device to enter the atmosphere of another planet, to make a soft landing on another planet and to return images from another planetary surface.
A computer-generated image showing New Horizons’ location in our solar system on August 10, 2019. The green line shows where the vehicle has travelled since its 2006 launch, the red indicates its future path. This perspective is from above the Sun and “north” of Earth’s orbit. Credit: JHU/APl

Since its flyby of the Pluto-Charon system, the New Horizons vehicle has continued its voyage out through the Kuiper Belt. Most of this has been with the vehicle in a state of hibernation to conserve power, however, in January 2019, the craft encountered  Kuiper Belt Object (KBO) Ultima Thule, aka 2014 MU69 (see my January 28th 2019 Space Sunday article), and data from that encounter is still being transmitted back to Earth.

Currently, the New Horizons mission is funded until April 2021, and may well be extended beyond that date. The vehicle’s radioisotope thermoelectric generator (RTG), which uses the heat from the radioactive decay of plutonium 238 to provide it with electrical power, is expected to provide sufficient energy for its science instruments until the mid-to-late 2030s. So the science team responsible for the mission at the John Hopkins University Applied Physics Laboratory are currently seeking potential KBO targets the craft could fly by in the mid or late 2020s.

Ultima Thule from a distance of 6,700 km, January 1st, 2019. Credit: NASA / JHU/APL / SwRI

Should the vehicle retain sufficient power for some of its instruments, it may be able to study the outer heliosphere (the “bubble” of space surrounding our solar system and created by the outward flow of energise particles from the Sun) in the late 2030s. If it does, it will add to the data gathered on that distant region of space, 100+ AU from Earth (1 AU = the average distance of the Earth from the Sun) by the Voyager spacecraft.

Parker Solar Probe: One Year In

August 12th, 2019, marked the first anniversary of NASA’s Parker Solar Probe. As I reported in Space Sunday: to touch the face of the Sun, this is an ambitious mission to repeatedly fly through the Sun’s corona – the hazardous region of intense heat and solar radiation in the Sun’s atmosphere that is visible during an eclipse – to gather data that could help answer questions about solar physics that have puzzled scientists for decades.

Named for Eugene Parker, the physicist who first theorised the solar wind, the constant outflow of particles and magnetic fields from the sun, the mission is now into its third orbit of the Sun, and due to make a further close solar approach on September 1st, 2019.

The spacecraft carries four suites of scientific instruments to gather data on the particles, solar wind plasma, electric and magnetic fields, solar radio emission, and structures in the Sun’s corona. This information will help scientists unravel the physics driving the extreme temperatures that make the corona hotter than the “surface” of the Sun – and the mechanisms that drive particles and plasma out into the solar system.

So much information has been gathered by the probe during its first two orbits of the Sun that the mission team on Earth is still analysing it. They hope to have the first results available before the end of the year – not that they are complaining!

We’re very happy. We’ve managed to bring down at least twice as much data as we originally suspected we’d get from those first two perihelion passes.

– Nicky Fox, director of NASA’s Heliophysics Division

An artist’s impression of the Parker Solar Probe swinging around the Sun at a distance of 6.2 million km (3.85 million mi) . Credit: NASA

Nor is that all; the probe’s elliptical 170-188 day orbit means that it has just 11 days per orbit in which to gather data – and these coincide with perihelion, when the craft must withstand temperatures of around 1,370ºC (2,500ºF). To achieve this, the probe is equipped with a 2.3m hexagonal solar shadow-shield that performs three tasks: it absorbs and reflects sunlight away from the vehicle whilst also preventing radiation penetrating its instrument bay and burning-out its circuits and instruments (incident solar radiation at perihelion is approximately 475 times the intensity at low Earth orbit) and also casting a long shadow in which the rest of the vehicle can remain relatively “cool”. Data on the shadow-shield and from within the vehicle as it passes through the corona reveal the shield is working better than anticipated.

So, with another six years of its planned 7-year primary mission, the Parker Solar Probe is set to revolutionise our understanding of the Sun’s corona and the mechanisms powering it.

The data we’re seeing is showing us details about solar structures and processes that we have never seen before. Flying close to the sun—a very dangerous environment—is the only way to obtain this data, and the spacecraft is performing with flying colours.

– Nour Raouafi, Parker Solar Probe project scientist, JHU/APL

Jupiter: of Origins and Collisions

Before NASA’s Juno mission, it was widely accepted that Jupiter’s core was dense and compact, somewhere between 5 and 20 Earth’s masses in size. However, data returned by Juno itself – which has as one of its goals, the probing the planet in an attempt to confirm what lies at its core – has proven to be somewhat confusing.

Rather than finding a solid central core to the planet, Juno’s data suggests Jupiter’s core is both extended and diluted, made up of rocky material, ice, hydrogen and helium that has no sharp transition between the presumed “solid” core and the surrounding gasses that make up Jupiter’s dense atmosphere. Such a “dilute” core is something astronomers have determined could not form naturally. So, what happened with Jupiter?

The answer, according to a study published in Nature in August 2019, appears to be that 4.5 billion years ago, a young Jupiter collided head-on with another embryonic planetary body in a similar orbit and roughly 10 times more massive than Earth. This giant impact caused the solid material of the original cores of Jupiter and the embryonic planet to shatter, mixing both with Jupiter’s gaseous atmosphere, resulting in the strangely diluted and elliptical core that still exists today.

An artist’s impression of the collision between a young Jupiter and a planetary embryo – and event that may have given rise to Jupiter’s unique core. Credit: Astrobiology Centre, Japan

The collision must have been head-on, because if the object didn’t hit Jupiter so directly, it would not have impacted with planet’s core and shatter it, but would have sunk slowly towards it, possibly eventually joining with it. Similarly, the protoplanet would have needed to have been around 10 times the mass of Earth because anything smaller wouldn’t have had sufficient mass to penetrate Jupiter’s atmosphere and strike the core with enough force to shatter both.

In addition, models of such a collision show that despite the passage of 4.5 billion years, there still hasn’t been sufficient time for all the perturbations it created to have fully abated and the material to settle into a more “regular” core with the expected differentiation between it and the surrounding atmosphere.