Space Sunday: of exoplanets and naming Charon’s features

Transiting Exoplanet Survey Satellite (TESS) – due to hunt for exoplanets potentially orbiting hundreds of thousands of stars around us. Credit: NASA’s Goddard Space Flight Center/CI Lab

On Monday, April 16th, 2018, after being delayed from a planned December 2017 lift-off, the launch window opens for NASA’s Transiting Exoplanet Survey Satellite (TESS).

As its name implies, TESS is designed to seek out exoplanets using the transit method of observation – looking for dips in the brightness of stars which might indicate the passage of an orbiting planet between the star and the telescope. Once in its assigned orbit and operational, TESS will work alongside the Kepler space observatory – now sadly nearing the end of its operational life and eventually the James Webb Space Telescope – in seeking worlds beyond our own solar system.

Roughly the size of an upright ridge/freezer combination, the 356 kg (800 lb) TESS is due to be launched on its way atop a SpaceX Falcon 9 booster from Launch Complex 40 at Canaveral Air Force Station, Florida, on April 16th, 2018, in a launch window that opens at 18:32  EDT (22:32 UT).  The rocket – sans it’s payload – underwent a static rocket motor test on Wednesday, April 9th, prior to it being returned to the launch preparation facility, where the Payload system and fairings containing TESS were mated to it in readiness for the launch. As well as launching TESS, SpaceX plan to recover the Falcon 9’s first stage.

The diminutive TESS satellite being enclosed in the Falcon 9 payload fairing at NASA’s Payload Hazardous Servicing Facility at Kennedy Space Centre prior to transfer to Canaveral Air Force Station for mating with the launch booster. Credit: NASA

Once on its way, Tess will take 60 days to reach its unique orbit, a “2:1 lunar resonant orbit“, which will allow the craft to remain balanced within the gravitational effects of the Moon and Earth, thus providing a stable orbital regime which should last for decades. In addition, the orbit means that TESS will be able to survey both the northern and southern hemispheres.

During this initial 60-period, scientists and engineers will spend the first week re-establishing contact with TESS and confirming its operational status as its instruments are cameras are powered-up. The instruments will then go through an extended commissioning and calibration phase, as engineers monitor the satellite’s trajectory and performance. After that, TESS will begin to collect and downlink images of the sky.

While Kepler has so far found the most exoplanets in our galaxy, it has done so by surveying relatively small arcs of the space visible to it. TESS, however, will do things differently. It will scan the galaxy in hundreds of light-years in all directions, a sphere of space containing some 20 million stars, paying particular attention to the brightest stars around us in the hope of detecting planetary bodies in orbiting them.

Left: The combined field of view of the four TESS cameras. Middle: Division of the celestial sphere into 26 observation sectors (13 per hemisphere). Right: Duration of observations on the celestial sphere. The dashed black circle enclosing the ecliptic pole shows the region which JWST will be able to observe at any time. Credit: NASA Goddard Spaceflight Centre

This will be achieved by dividing space into 26 individual “tiles”, allowing the four imaging systems on the craft to repeatedly observe a “strip” of four tiles at a time for a minimum of 27 days each (and parts of some for up to a year at a time) before moving to the next strip, working its way around the sky. In this way, it is estimated TESS will be able to survey up to 200,000 stars in both the northern and southern hemispheres over multiple years.

Amid this extrasolar bounty, the TESS science team aims to measure the masses of at least 50 small planets whose radii are less than four times that of Earth. Many of TESS’s planets should be close enough to our own that, once they are identified by TESS, scientists can zoom in on them using other telescopes, to detect atmospheres, characterize atmospheric conditions, and even look for signs of habitability.

In this latter regard, TESS will pave the way for detailed studies of candidate exoplanets by the James Webb Space Telescope (JWST), now scheduled for launch in 2020. While TESS cannot look for atmospheric or other signs of life on the distant worlds it locates, JWST will be able to do just that. So, even as we prepare to say a sad goodbye to Kepler, the hunt of exoplanets is actually just hotting up.

Proxima b: Another Blow to Its Potential to Harbour Life

Proxima b, the closest exoplanet to our solar system – a “mere” 4.25 light years away from the Sun as it orbits our nearest stellar neighbour, Proxima Centauri, has been the subject of much speculation as to it likely atmospheric and surface conditions since its existence was confirmed in August 2016.

The chances of the planet being the abode of life always tended to look unlikely. Proxima Centauri is a M-type red dwarf star, roughly one-seventh the diameter of our Sun, or just 1.5 times bigger than Jupiter. Such stars are volatile in nature and prone stellar flares. Given the proximity of Proxima b – just  7.5 million km (4.7 million miles) from its parent, it is entirely possible such flares could at least heavily irradiate the planet’s surface, if not rip away its atmosphere completely, leaving it lifeless, despite the fact it sits within Proxima Centauri’s “Goldilocks zone” where conditions might be “just right” for life to gain a foothold on a world.

The Earth-sized Proxima-B and its parent star

A new report concerning Proxima Centauri – coming on top of one issued in March (see here) – lends further weight to the solar flare argument. The First Naked-Eye Superflare Detected from Proxima Centauri, analyses the likely outcome of a high-energy “superflare” that erupted from Proxima Centauri, which was so powerful, it was “visible to the naked eye” (through a telescope), which was recorded here on Earth in March 2016.

This flare was observed by the Evryscope, an array of telescopes that is pointed at every part of the accessible sky simultaneously and continuously. While multiple studies have been carried out on low- and moderate-energy flare events on Proxima, the Evryscope observation marked the first time a high-energy event has been recorded – and it was massively powerful, as the team behind the study report:

In March 2016 the Evryscope detected the first-known Proxima superflare. The superflare had a bolometric energy of 10^33.5 erg, ~10× larger than any previously detected flare from Proxima, and 30×larger than any optically measured Proxima flare. The event briefly increased Proxima’s visible-light emission by a factor of 38× averaged over the Evryscope’s 2-minute cadence, or ~68× at the cadence of the human eye. Although no M-dwarfs are usually visible to the naked-eye, Proxima briefly became a magnitude-6.8 star during this superflare, visible to dark-site naked-eye observers.

Confirmation of the superflare came from the Pale Red Dot campaign – responsible for revealing Proxima b – using the HARPS spectrograph , a part of the 3.6 metre telescope at the ESO’s La Silla Observatory in Chile. By combining the Evryscope data with that gathered by HARPS the research team were able to constrain the superflare’s UV spectrum and any associated coronal mass ejections.

Then, using data gathered by Evryscope, the team mapped 23 other large Proxima flares, ranging in energy from 10^30.6 erg to 10^32.4 erg occurring over a period of the last two years and applied the constraints to each of them to create a model to determine what effects this star would have on a nitrogen-oxygen atmosphere, including how long the planet’s protective ozone layer would be able to withstand the blasts, and what effect regular exposure to radiation would have on terrestrial organisms.

The conclusion: any planets orbiting Proxima Centauri would not be habitable for very long. In all probability, the surface of Proxima b was exposed to lethal radiation even as the atmosphere was slowly peeled away over the aeons by repeated exposure to solar activity.

This study has implications for other M-type star systems, which make up about 75% of the galaxy. As it lays out, around two-thirds of these stars experience active flare activity which could affect the planets orbiting them. Thus, measuring the impact that superflares have on these worlds will be a necessary component to determining whether or not exoplanets found by future missions are habitable.

Looking ahead, the team hopes to use the Evryscope to examine other star systems, particularly those that are targets for the upcoming TESS mission, further helping scientist to assess their activity and the impact it might have on any planets revealed to be orbiting them.

 NASA May Extend Space Station Rotations

In my previous Space Sunday update, I noted that NASA is considering making the second test flight of Boeing’s CST-100 commercial crew transport effectively an operational flight. The reason for this is to help remove further reliance on using Russia’s Soyuz vehicles to maintain access to the International Space Station (ISS) beyond the current agreement with Russia. It has now been confirmed that the US space agency is additionally considering extending crew missions to the station.

The International Space Station, circa 2007. Credit: NASA

NASA’s current agreement with flying astronauts on Soyuz vehicles expires in 2019. By that time, both the Boeing CST-100 and the SpaceX Dragon 2 should have started flying crews two and from the ISS. However, there are concerns that any delays in the commercial vehicle programme could impact the availability of one or other of the two vehicles. Extending the length of time crews spend aboard the ISS with each rotation – currently 6 months – could be a way of compensating for any lack of certified crew vehicles to handle transfers.

Exactly what any extension to rotation periods might be hasn’t been made clear. It’s also currently unclear on what technical issues might be involved in extending ISS mission durations, such as potential problems in how long a Soyuz spacecraft can remain docked to the ISS.

 Charon’s Surface Features Gain Names

In 2015, NASA’s New Horizons spacecraft made history by being the first spacecraft to fly through the Pluto-Charon system, returning a huge amount of data and images about both of these remote worlds, revealing them  to be places of the unexpected.

Until now, most of the attention has been on Pluto, a world of unique contrasts and exhibiting conditions and processes no-one ever expected to find. However, the IAU Working Group for Planetary System Nomenclature has now officially approved a dozen names proposed by the mission team for surface features on Charon. These names include science fiction authors Arthur C. Clarke and Octavia Butler.

The official names for some of Charon’s surface features, as approved by the International Astronomical Union (IAU). Credit: IAU

Sir Arthur C. Clarke is honoured and remembered through the Clarke Montes. Film director and producer Stanley Kubrick, with whom he collaborated on the iconic 2001: A Space Odyssey, is similarly honoured with a mountainous region named for him, as is America science fiction author Octavia E. Butler, the first science fiction writer to win a MacArthur fellowship.

In addition, a number of features were named after fictional characters from famous stories and folklore. The massive depression of Dorothy Crater is named for L. Frank Baum’s heroine from The Wizard of Oz, Nemo Crater takes its name from the captain of the Nautilus in Jules Verne’s 20,000 Leagues Under The Sea (and not a small animated fish from Disney Studios…). Meanwhile the Revati Crater is named in honour of the main character in the Hindu epic narrative Mahabharata, and the Nasreddin Crater is named for the protagonist in thousands of folktales told throughout the Middle East and Asia.

These names were all put forward by the New Horizons team as part of a much large selection of names they have been informally using to identify feature on Charon – many of which were drawn from popular science fiction TV and film series, such as Star Trek, Firefly, Doctor Who, Star Wars, Macross and Alien. These include “Ripley Crater” and “Nostromo Chasma” (Alien), the “Vulcan Planum” with the “Kirk”, “Spock”, “Uhura” and “Sulu” caters (Star Trek) and the “Organa”, “Skywalker” and “Vader” craters (Star Wars).

Some of the informal names used by the New Horizons mission team to denote surface features on Charon. Credit: New Horizons Mission team

All of the names – informal and formal – were submitted by both team members and the general public as a part of the Our Pluto campaign. As submissions to the IAU, some of the remaining informal names may yet gain approval.

Since its passage through the Pluto-Charon system, New Horizons, one of the fastest man-made objects travelling through the solar system – is passing deeper into the Kuiper Belt, the circumstellar disc of asteroid-like rocks extending outward from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. On January 1st, 2019, the space craft will pass the Kuiper Belt object (KBO) dubbed “Ultima Thule” (“beyond Thule” or “beyond the known world”) and officially known as 2014 MU69. At 1.6 billion kilometres (1 billion miles) beyond the orbit of Pluto, the flyby will be the farthest planetary encounter in history, with “Ultima Thule” the most primitive object ever observed by a spacecraft.


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