Space Sunday: other worlds, near and far

Curiosity on “Mount Sharp” as seen by the Mars Reconnaissance Orbiter. Credit: NASA/JPL / MSSS  (click for full size)

NASA’s Mars Science Laboratory rover, Curiosity continues to climb Aeolis Mons (“Mount Sharp”), and in doing so, it has been once again imaged from orbit by the HiRISE camera system on NASA’s Mars Reconnaissance Orbiter (MRO). The image was captured on June 5th, 2017 (Curiosity’s 1717th Martian Sol), at the same time the rover was engaged in taking colour images of its surrounding using its mast-mounted Navcam system.

MRO has actually been imaging Curiosity roughly once every three months, as the orbiter’s track around Mars carries it over “Mount Sharp” and the rover’s route up the mound’s flank. However, these aren’t simply happy snaps of the rover’s progress: MRO is actively monitoring the terrain around the rover to allow scientists to check for changes – such as movement among sand dunes – and to help plan the rover’s route up the slopes.

The June 5th image, released by NASA on June 20th, has been colour enhanced to better reveal Curiosity as a bright blue feature. To give an idea of scale and resolution, the rover is some 3 metres (10ft) in length and 2.8 metres (9 ft) wide.

A mosaic of images captured by Curiosity using the Navcam system, looking back along the rover’ route up “Mount Sharp” towards the distant rim of Gale Crater. The images making up the view were all captured on June 5th, 2017 (Sol 1717 for the rover), the same day as MRO imaged the rover from orbit. Credit: see image

Curiosity is currently traversing ground between two points of scientific interest: the “Bagnold Dunes”, an area of sand dunes which are slowly progressing down the side of “Mount Sharp” as a result of both wind action and gravity; and a high-standing ridge which runs parallel to the eastward side of the dune field. Dubbed the “Vera Rubin Ridge” after the American astronomer who pioneered work on galaxy rotation rates, this ridge line is of interest to scientists because it has been shown to exhibit signatures of hematite, an oxidized iron mineral which can provide clues to the environmental conditions on this region of “Mount Sharp” when it formed.

The route to the ridge is slightly circuitous. At the moment the rover is heading east-north-east around a small set of dunes. Once clear of them it will turn south-east and drive to where a potential safe route up onto the ridge has been identified. The drive is further slowed as Curiosity periodically pauses to capture images of the feature to help scientists characterize any observed layers, fractures, or geologic contacts and better understand determine how the ridge formed, and its relationship to the other geologic units found within Gale Crater.

The route ahead: a June 14th (Sol 1726) mosaic captured by Curiosity, showing “Vera Rubin Ridge”, which was roughly 370 metres (114 ft) away from the rover at the time the images were captured. Credit: NASA/JPL / MSSS / Ken Kremer / Marco DiLorenzo

At the same time NASA released the image of Curiosity seen from orbit, half a world away, attempts to correct a wheel problem the solar-powered Opportunity Mars Exploration Rover (MER) had been experiencing appeared to end in partial success.

“Oppy” had suffered a failure with its left-front wheel steering actuator on June 4th, leaving the wheel angled and unable to straighten. After numerous attempts to correct the issue, a new approach tested on June 20th resulted in the wheel turning correctly and resuming its proper alignment with the other wheels. However, what originally caused the actuator to fail remains unknown, and there is concern that it might recur.

To limit the risk of this happening and possibly stranding “Oppy”, the rover will avoid all use of its front wheel steering, and will only use its rear wheel steering when absolutely necessary. To maintain manoeuvrability, it will instead rely on “tank steering” – effectively running the drive motors for the wheels on one side of the rover in opposition to those on the other, allowing Opportunity to turn left or right more-or-less on the spot, a technique the rover is designed to use. This should allow the rover to continue its current survey of “Perseverance Valley” in preparation for a descent into Endeavour Crater.

“Planet Nine” Set to Become “Planet Ten”?

I’ve written extensively in these pages about the hunt for “Planet Nine” (or “Planet X” or “George”, “Jehoshaphat” or “Planet of the Apes” as some would have it): the Neptune-sized world believed to be orbiting the sun at a distance of at least 200 astronomical units (AUs – one AU being the average distance of the Earth from the Sun) in a highly eccentric orbit.  The search for that world is still continuing, but if a new study is confirmed, that mystery world may well have to give up its “Planet Nine” title for another.

A planetary mass object the size of Mars would be sufficient to produce the observed perturbations in the distant Kuiper Belt. Credit: Heather Roper/LPL

Kat Volk and Renu Malhotra of the University of Arizona’s Lunar and Planetary Laboratory, offer compelling evidence of a yet-to-be-discovered planetary body with a mass somewhere between that of Mars and Earth, orbiting the Sun much closer than the mysterious “Planet Nine”, at around 50 AU distance.

Whilst carrying out a detailed studying of Kuiper Belt Objects (KBOs) – the disk of rocky asteroids and comets surrounding the Sun from a distance of around 30 AU to about 50-60 AU, Volk and Malhotra discovered a consistent anomaly. Whilst most KBOs surround the sun with orbital inclinations that average out to what planetary scientists call the “invariable plane of the solar system”, they discovered that the more distance KBOs – those around 50 AU or over from the Sun are tilted away from the invariable plane by about eight degrees.

The pair surveyed around 600 of the 2,000 observed KBOs, and found all of those on the outer reaches of the Kuiper Belt to be inclined from the invariable plane by roughly the same amount and in numbers that tend to preclude a statistical fluke. In modelling possible causes for this, they discovered that an object with a mass of Mars, orbiting about 50-60 AU would cause just such a disruption, as would a Earth-sized body slightly further away.

However, Volk and Malhotra carefully avoid any suggestion there is a Mars- or Earth-sized body is awaiting discovery, noting that the disruption might also be the result of several large (but not planet-sized) masses lying within the outer fringes of the Kuiper belt. Even so, a single body would seem more likely, and given it is effectively sitting within the galactic plane – an area so densely packed with stars that solar system surveys tend to avoid it – could explain why it has been able to remain undetected.

An artist’s rendering of the LSST atop Cerro Pachón mountain, Chile. When LSST starts taking images of the entire visible southern sky in 2022, it will produce the widest, deepest and fastest views of the night sky ever observed. Over a 10-year time frame, LSST will image several tens of billions of objects and create movies of the sky with unprecedented detail – and might reveal whatever is causing the odd perturbations among the KBOs studied by Volk and Malhotra. Credit: Large Synoptic Survey Telescope Project Office

But it might not remain hidden for much longer. 2020 should see the Large Synoptic Survey Telescope (LSST) come on-line. This 8.4 metre (27.6 ft) primary mirror telescope is due to commence a 10-year sky survey in 2022. Among other things, it is expected to increase the number of KBOs so far observed from 2000 – to over 40,000 as it carries out real-time surveys of the sky, night after night. In doing so, it could well find any planet-sized body lurking near them.

Russia to Partner China in Space Station Project?

In April it was reported in some quarters that Russia might be ready to ditch the International Space Station in 2024 – that’s the year the United States has indicated it might hand over the facility to private sector operations (although there have also been discussions on extended the ISS mission through to 2028). At that time, it was suggested by Russian officials that they might be in talks with China regarding Chinese plans for an orbiting space station.

Roscosmos head Igor Komarov

Speaking at the Paris Air Show on Monday, June 19th, the head of Russia’s  Roscosmos State Corporation for Space Activities, Igor Komarov, indicated that those discussions are still continuing, with both parties putting proposals to one another which include possibly operating a joint space station venture.

Speaking to reporters at Le Bourget – and while acknowledging that Russia and  China have a long way to go before they reach a formal agreement on anything, Komarov stated that are areas of broad agreement between the two nation vis space, and that when it comes to space stations,”it makes no sense to go it alone; that it’s necessary to create it together.”

Asked whether Russia would benefit from cooperating with China in the construction of a new space station, Andrei Ionin, a member of the Tsiolkovsky Russian Academy of Cosmonautics, said that in the context of deteriorating relations with Russia’s Western partners, and the Russian space programme’s financial difficulties, cooperation with the Chinese is essential. Nor would it be particularly new.

In the mid-1994, Russia sold some of its advanced aviation and space technology to the Chinese government, including Soyuz spacecraft technology, which helped the Chinese in the development of their Shenzhou (“divine vessel”) spacecraft. Russia also helped train early groups of Chinese taikonauts.  Certainly, a partnership with Russia – with decades of experience with its Salyut and Mir space stations prior to joining the ISS project – would of of huge benefit to China

There are some practical issues which would need to be sorted out were the two nations to attempt to jointly operate a space station. For one thing, the locations of their respective launch facilities mean that each country has a different optimal orbital inclination for Earth-orbiting operations: Russia launches its space vehicles into orbit at an inclination of 51.6 degrees; China at an inclination of 40 degrees. While these differences do not limit joint orbital operations per se, they do mean that were one selected over the other, the country “losing out” on their preferred orbital inclination would also have a reduced role in resupply and support missions for the station, potentially making them something of a “junior partner” in the venture.

Might the Chinese and Russia work together on a future space station, rather than China going it alone? Russian officials suggest the two are stronger together, and that plans are being hammered out towards possible agreements. Credit: CCTV

Nor is China isn’t the only partner Russia is considering for future operations in Earth orbit. In May, Russian Deputy Prime Minister Dmitri Rogozin instructed Roscosmos to look into the possibility of developing a space station capability beyond the ISS in cooperation with the entire BRICS (Brazil, Russia, India, China and South Africa) group of nations, again as a result of souring relations with Europe and America.

Kepler Reveals 10 More Earth-Sized Exoplanets – And More

On Monday, June 19th, NASA published the latest update to the Kepler exoplanet catalogue, introducing 219 new exoplanet candidates in the process 10 of which are near-Earth size and orbiting in their star’s habitable zone.

The latest iteration of the Kepler catalogue, drawn from the observations of the Kepler Space Telescope, is the eighth such publication since the mission started in 2009, and it is also the most comprehensive. It contains 4,034 planet candidates identified by Kepler, of which, 2,335 have been verified as exoplanets. Out of these 2,335, around 50 have been denoted as Earth-sized candidates orbiting in the habitable zone around their parent star – and more than 30 of these have been verified.

For the first four years of its primary mission, the space telescope observed a set star field located in the constellation Cygnus Since 2014, Kepler has been collecting data on its second mission, observing fields on the plane of the ecliptic of our galaxy. Credit: NASA / Wendy Stenzel

As with all planets detected by Kepler, the 219 new discoveries were all made using the transit method. This consists of monitoring stars for occasional dips in brightness, which is used to confirm the presence of planets transiting between the star and the observer. Before publishing the survey, the science team carried out tests to eliminate false positives and to ensure they hadn’t missed any potential candidates, first by introducing simulated transits into the dataset to make sure the dips that Kepler detected were consistent with planets. Then they added false signals to see how often the analysis mistook these for planet transits.

This led to another exciting find, which was the indication that for all of the smaller exoplanets discovered by Kepler, most fell within one of two distinct groupings. Essentially, half the planets that we know of in the galaxy are either rocky in nature and larger than Earth (i.e. Super-Earths), or are gas giants that are comparable in size to Neptune (i.e. smaller gas giants). This could have significant implications in the search for habitable planets and extra-terrestrial life, as Mario Perez, Kepler programme scientist noted at the press conference announcing the catalogue’s publication.

“The Kepler data set is unique, as it is the only one containing a population of these near Earth-analogues – planets with roughly the same size and orbit as Earth,” he said. “Understanding their frequency in the galaxy will help inform the design of future NASA missions to directly image another Earth.”

Small planets come in two sizes: a histogram showing the number of planets per 100 stars as a function of planet size relative to Earth. Credit: NASA/Ames Research Centre / CalTech/ University of Hawaii / B.J. Fulton

Several of the newly discovered planet candidates orbit G dwarf stars like our sun and occupy their star’s habitable zones – like KOI-7711 (KOI meaning Kepler Object of Interest). Around 1.3 times the size of Earth, it orbits it parent star once every 302 days, and receives roughly the same amount of heat that we get from our own star. However, this doesn’t mean it is necessarily Earth-like and supports life. The Sun really has three planets in its habitable zone – but you wouldn’t want to try living unprotected on Mars, or on Venus at all.

But Kepler’s updated exoplanet listing will help astronomers estimate how common rocky, potentially habitable planets are in our galaxy. Kepler has already revealed, for example, that roughly one in four  M-class dwarf stars, which make up around 75% on the stars in the galaxy, is orbited by a small planet in the habitable zone. While this doesn’t, in any way give us any definitive answer to the question of “are we alone?”, the more small, “earth-sized” solid worlds we find within the habitable zones of other stars, the greater the potential for at least some of them to have given rise to life, however basic, becomes.