Space Sunday: exoplanets and launch systems

An artist’s impression of Ross 128. Credit: ESO / M. Kornmesser

The European Southern Observatory (ESO), responsible for finding a planet orbiting the Sun’s nearest stellar neighbour, Proxima Centauri (see here for more), has now discovered another exoplanet orbiting a nearby star.

The star in question is Ross 128, a red dwarf located in the constellation of Virgo. As I’ve previously noted, red dwarf stars tend to be extremely violent in nature. Their internal action is entirely convective, making them unstable and subject to powerful solar flares, generating high levels of radiation in the ultraviolet and infra-red wavelengths which can leave planets like the one orbiting Proxima Centauri or those orbiting TRAPPIST-1 unlikely to support life.

However, Ross 128 is different. It is a “quiet” red dwarf; it experiences less in the way of flare activity, meaning any planets orbiting it will be exposed to less radiation and stellar wind. In particular, the planet discovered by ESO could potentially be habitable.

The planet, designated Ross 128 b, was discovered using the ESO’s High Accuracy Radial velocity Planet Searcher (HARPS), located at the La Silla Observatory in Chile. HARPS uses measurements of a star’s Doppler shift in order to determine if it moving back and forth, a sign that it has a system of planets. The data gathered by the instrument allowed astronomers to confirm Ross 128 b is a rocky world, with roughly 35% more mass than Earth, orbiting Ross 128 at a distance of about 0.05 AU, and with a period of 9.9 Earth days.

Measurements of Ross 128’s likely radiative output, combined with the planet’s distance from the star put it on or near the star’s habitable zone – the region around a star where a solid body planet might have both an atmosphere and liquid water on the surface. It receives around 38% more light from its star than Earth does from the Sun. This has allowed the team making the discovery to estimate that Ross 128 b’s equilibrium temperature is likely somewhere between -60 °C and 20 °C – close to what we experience here on Earth, making it a temperate planet.

That Ross 128 is a “quiet” older red dwarf, less prone to violent outbursts, means Ross 128 b may well have retained any atmosphere which may have formed around it. Whether or not Ross 128 b has an atmosphere has yet to be determined; if it does, given the planet is likely to be tidally locked, with the same same side always facing towards its star, any atmosphere the planet may have could be subject to extreme weather.

Even so, given what is currently known about Ross 128 b, were it to have an atmosphere and liquid water on the surface, it would be the closest potentially habitable exoplanet to Earth so far discovered. This alone means Ross 128 b is liable to be the subject of a lot of additional study over the coming months.

Nor is this the first time Ross 128 has been in the news this year. In July 2017, Abel Méndez, an astrobiologist at the Arecibo Radio Telescope, reported that on May 12th, 2017, during a 10-ten observation of Ross 128, the telescope received a 10-minute wide-band radio signal “almost periodic” in natures, and which decreased in frequency.

While some were quick to link this event with the November discovery of Ross 128 b, it’s worth pointing out that Arecibo, the Green Bank Telescope in West Virginia and the Allen Telescope Array (ATA) in northern California, have all spent time listening to Ross 128 without any of them hearing any repeat of the signal. Currently the most widely accepted explanation for the May 2017 signal is radio frequency interference from a satellite orbiting the Earth.

A Lava World with an Atmosphere?

And staying with exoplanets, 55 Cancri e, also named Janssen, has also been in the news this week.

One of the few exoplanets discovered prior to the Kepler mission, it is one of five planets orbiting 55 Cancri A, the G-class main sequence star which forms one half of the binary star system 55 Cancri, some 41 light years away from the Sun, in the constellation of Cancer. At 7.8 Earth masses, and with a diameter almost 50% that of Neptune, it has the distinction of being the first “super-Earth” discovered in orbit around a main sequence star similar to the Sun.

An artist’s impression of super-Earth exoplanet 55 Cancri e and its parent star. Credit: NASA/JPL

Discovered in August 20o4, the planet has been subject of extensive study. As the closest planet to its parent, it takes 2.8 days Earth days to complete one orbit, and is tidally locked, always keeping the same side facing its parent. A study of the planet using the Spitzer space telescope in 2013 led astronomers to the conclusion 55 Cencri e is likely carbon planet, dominated by lava flows on its sunward side. In 2016, observations using the Hubble Space Telescope indicated the planet may have a thin hydrogen and helium atmosphere with suggestions of hydrogen cyanide.

However, an international team led by Cambridge University in the UK, has been re-examining the data gathered by the Spitzer space telescope. Using an improved model of how energy would flow throughout the planet and radiate back into space, their findings indicate that temperatures on the “dark” side of the planet average 1,300 to 1,400 oC (2,400 to 2,600 oF), much closer to to the average 2,300 oC (4,200 oF) on the sunward side than previously thought.

These finding suggest 55 Cancri e has a far denser, more complex atmosphere than had been thought, one which acts as transfer mechanism for circulating heat around the planet. What’s more, this atmosphere may well contain nitrogen, water vapour and even oxygen—molecules found in our atmosphere, too—but with much higher temperatures throughout.

The overall conditions on the surface of the planet preclude free-flowing water or the opportunity for life to arise, but they also present a further mystery. Given its proximity to its parent star, in theory 33 Cancri 2e’s atmosphere should have been stripped away aeons ago by the solar wind. so there are still mysteries with the planet yet to be resolved.

The Eccentric Exoplanet

And finally for exoplanets this week, astronomers have discovered one in a highly elliptical orbit around an ancient star which could help us understand more about how planetary systems form and evolve over time.

HD76920b, a planet with four times the mass of Jupiter, is in a highly elliptical orbit around a star some 2 billion years older than our own Sun, and some 587 light years away from Earth in the southern constellation Volans. Were its orbit to be overlaid on a map of the solar system, it would come within the orbit of Mercury and extend out beyond the orbit of Mars.

The orbit of HD76920b superimposed on a model of the solar system. Credit: Jake Clark

Planets with eccentric orbits have been found before, although they are rare. What is unusual about HD76920b is that as a gaseous planet, it will change shape as it swings past its star, stretched by its enormous gravity. Over time, this tidal interaction should have resulted in the planet’s orbit being circularised, gradually pull the most distant point of the planet’s orbit inwards. Given the overall age of the star in question, this should have happened a very long time ago; as it hasn’t suggests HD76920b cannot have occupied its current orbit since its birth.

One explanation for this is that the star may once have had more planets in near-circular orbits around it. Over time these planets nudged one another around gravitationally, creating a chaotic architecture which saw most of them scattered into deep space, leaving just one – HD76920b – pushed and pulled by the others into its elliptical orbit.

Whether or not this is an accurate theory is impossible to know. But there is one thing that is known about  HD76920b; its parent star is approaching the end of its life. In the next few million years, will expand as it uses its nuclear fuel. ‘ds parent star will swell as it comes to the end of its life. When this happens, the planet may be pulled apart due to increasing gravitational stresses as it swings close to the star – or it will be devoured.

Virgin Orbit Secures Military Contract

Virgin Orbit, the commercial launch spin-off of Sir Richard Branson’s Virgin Galactic, has announced it has secured a military launch as its first contract, and the flight will likely take place in January 2019.

The company’s LauncherOne rocket is designed to lift payloads of between 200 kg and 230 kg (440 lb and 500 lb), depending on the mission profile. The rocket is intended to be lifted aloft by a 747 carrier aircraft to an altitude of 10,800 metres (35,000 ft) before being released to use its own engines to lift payloads to their assigned orbits.

An artist’s impression of Cosmic Girl, as it had been expected to look in its Virgin Galactic livery, having just released a LauncherOne vehicle. Credit: Virgin Orbit

On November 16th, 2017, the company indicated the 2019 launch will carry a selection of Space Test Program payloads on behalf of the U.S. Air Force’s Space Test Program partnered with the US Defense Innovation Unit Experimental (DIUx).

The contract came after six months of negotiations, and with it Virgin Orbit announced the formation of a US subsidiary, VOX Space, which will focus on national security space customers for LauncherOne. The company will handle the management, engineering, and related services needed for government customers flying on LauncherOne; its formation was necessary to overcome Virgin Orbit, whilst based in the United States, being a foreign-owned company.  Virgin Orbit was itself spun-off from Virgin Galactic in March 2017.

A LauncherOne test article — an entire vehicle except for payload fairing and fins — leaves Virgin Orbit’s Long Beach, California, factory for integrated stage testing. Credit: Virgin Orbit

Ahead of the launch, Virgin Orbit will be conducting a series of tests of the system. These will involve the 747 carrier aircraft (originally called Cosmic Girl when part of the Virgin Atlantic fleet) with dummy LauncherOne payloads, as well as static engine tests of the LauncherOne rocket itself. This will culminate in a full test flight of the combined system in early 2018, with the LauncherOne carrying a dummy payload into orbit.

Zuma, the Secret Satellite Without an Owner, Launch Delayed

In my previous Space Sunday article, I noted that SpaceX was aiming for an ambitious end to 2017, with no fewer  than five launches before the end of the year – including the maiden flight of their new Falcon Heavy booster. However, these plans have now been dealt a blow: SpaceX has suspended all further launches pending the review of data from a recent payload fairing test.

The Falcon 9 rocket due to lift the super-secret “Zuma” mission into space, sitting at Lauch Complex 39A, Kennedy Space Centre, on November 16th, 2017. Credit: SpaceX

Another SpaceX launch affected by the suspension is that of the super-secret “Zuma” spy satellite, which had been scheduled for launch on Friday, November 17th, 2017 atop a Falcon 9 rocket.

Due to lift-off from Kennedy Space Centre, the “Zuma” mission has been a source of intrigue because no-one in the US intelligence and defence communities appears to own it – not even the National Reconnaissance Office.

All that is known about the mission is that the launch contract was arranged as a commercial enterprise under the auspices of Northrop Grumman Corporation to “significantly slash launch costs for whatever U.S government entity is responsible for “Zuma”, and the payload is intended for low-Earth orbit operations no more than around 2,000 km (1,200 mi).

Not typically considered one of a rocket’s most complex or high-risk systems, payload fairing assemblies are nonetheless critical to a mission’s success.  They protect satellites from the stresses of a rocket’s climb through the atmosphere, including aerodynamic pressure, weather, heating, and the rocket’s own vibrations.  However, if the payload fairing elements fail, they can prevent a satellite from deploying in the right orbit, or from reaching orbit at all.

Currently, SpaceX haven’t indicated whether or not there is a problem with their payload fairings – which are manufactured by the company. All that has been stated is that the decision was taken after carrying out tests on a fairing assembly intended for another customer.

Dream Chaser’s Flight

Also in my previous Space Sunday article, I reported on the second free flight test for Sierra Nevada Corporation’s Dream Chaser test article on November 11th, 2017. The company subsequently released a video of the test, which I’ve embedded below.