I’ve written a lot about Planet Nine, the mysterious, yet-to-be-discovered world thought to be orbiting far out in the hinterlands of the solar system, and potentially responsible for the odd orbits of a number of bodies in the Kuiper Belt (referred to as Kuiper Belt Objects, or KBOs). Most recently – in June 2018 – I noted that one field of research suggested that while gravity could be responsible for the eccentric orbits seen with many KBOs, it might not have anything to do with the presence of another planet.
Now a new study – Shepherding In A Self-Gravitating Disk Of Trans-Neptunian Objects – further casts doubt on – but does not eliminate – the need for any planetary object being responsible for the odd orbits of Sedna and the other unusual KBOs. In it Professor Jihad Touma, from the American University of Beirut, and Antranik Sefilian, a PhD student in Cambridge’s Department of Applied Mathematics and Theoretical Physics, suggest a disc of icy material could be the cause.
The attraction for there being a planet responsible for teasing these objects into the odd orbits is that over the last 15 years, some 30 Trans-Neptunal Objects (TNOs) have been discovered in highly-elliptical orbits, all of which would appear to a large planetary object having some form of influence on them. However, despite extensive attempts to locate this mysterious body, possibly the size of Neptune, it has remained elusive – possibly because it doesn’t exist.
The Planet Nine hypothesis is a fascinating one, but if the hypothesised ninth planet exists, it has so far avoided detection. We wanted to see whether there could be another, less dramatic and perhaps more natural, cause for the unusual orbits we see in some TNOs. We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disc beyond the orbit of Neptune and see what it does for us?
– study co-author Antranik Sefilian
Instead, he and Touma modelled the full spatial dynamics of TNOs, taking into consideration the influence of the known giant outer planets in the solar system and a massive, extended disc of material beyond Neptune. Their results suggest that such a large – if yet-to-be-discovered – disc of material were to be orbiting the Sun at a great distance, it could give rise to TNOs occupying highly elliptical and exaggerated orbits around the Sun. In addition, they were able to model mass ranges and shapes for the icy disc and demonstrate how gradual shifts in its precession rate, could give rise to the wilder orbits seen with the 30+ eccentric TNOs.
If you remove planet nine from the model and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs.
– study co-author Antranik Sefilian
However, there is a problem with the theory – or two issues at this point in time. The first is that, like Planet Nine itself, it’s one things developing a computer model that demonstrates of a disc of distant material can influence TNOs and drive them into strange orbits, it is quite another to physically find it. The second is that attempts thus far made to estimate the mass of icy objects beyond Neptune have only added up to about one-tenth the mass of Earth – which is far too little to have any significant influence over TNOs. Part of the problem here is that as we’re inside the disc and looking out at it, it is incredible hard to sport the material that might be a part of it – something which Sefilian and Touma acknowledge.
But there is more than enough evidence found around other solar systems to suggest extended discs of icy material are actually quite commonplace, and so one could well by surrounding our own. What’s required is a longer, more considered look and the space around us – something that may well take time. And even then, Touma and Sefilian acknowledge that while their study suggests there is no need for any mystery planet, the hunt for Planet Nine shouldn’t be entirely abandoned; it might be that both it and a distant icy disc of objects might be responsible for the “rogue” TNO orbits far outside the plane of the ecliptic.
New Horizons Returns Best View Yet of Ultima Thule
On January 25th, 2019 NASA and John Hopkins University revealed the most stunning picture of Ultima Thule thus far returned by the New Horizons mission as it flew by the Kuiper Belt object (KBO) on January 1st, 2019.
Obtained with the wide-angle Multicolor Visible Imaging Camera (MVIC) the image was captured when New Horizons was just 7 minutes from its point of closest approach to the KBO, and just 6,700 km (4,200 mi) from it. With an original resolution of 440 feet (135 meters) per pixel, the image was stored in the spacecraft’s data memory and transmitted to Earth on January 18th/19th, where it went through a process designed to sharpen the image and enhance fine detail.
The oblique lighting of this image reveals new topographic details along the terminator, near the top. These details include numerous small pits up to about 0.7 km (0.4 mi) in diameter. The large circular feature, about 7 km (4 mi) across on the smaller of the two lobes, also appears to be a deep depression. It’s currently unclear whether these pits are impact craters or features resulting from other processes, such as “collapse pits” or the ancient venting of volatile materials.
This new image is starting to reveal differences in the geologic character of the two lobes of Ultima Thule, and is presenting us with new mysteries as well. Over the next month there will be better colour and better resolution images that we hope will help unravel the many mysteries of Ultima Thule.
– Alan Stern, New Horizons Principal Investigator
Commercial Spaceflight: Rapid Round-up
Virgin Galactic Let 40 Staff Go, Expect to Start Commercial Flight Mid-2019
On the heels of SpaceX announcing they are shedding some 10% of their workforce, Virgin Galactic has indicated it has laid off some 40 staff – or about 5% – of its own workforce. The move was described as being part of a realignment of skill sets as the company prepares to shift to commercial operations later this year.
Most of the affected employees were at the company’s facilities in Mojave, California, where it is building and testing its SpaceShipTwo suborbital spaceplane. Their departure will not will not affect plans to continue testing SpaceShipTwo, with the next flight expected to take place the coming weeks.
In an interview with CBS This Morning on January 24th, 2019, Virgin Galactic founder Sir Richard Branson indicated there will likely be around three more test flights over the next several months, after which operations will shift to the Mojave Air and Space Port in readiness to start commercial operations, most likely in July.
I will hope to go up in the middle of this year myself. We’ve got another test flight in a handful of weeks taking place from Mojave, then we’ll have another one a few weeks later, then another one. And then, we move everything to New Mexico where we have a beautiful spaceport.
– Sir Richard Branson, CBS Good morning, January 24th
Another company moving towards flying fare-paying passengers on sub-orbital hops is Blue Origin, founded by Amazon Kingpin Jeff Bezos. On January 23rd, after number of delays, the company completed the 10th test flight of its New Shephard launch vehicle and capsule system.
Lifting-off from the company’s West Texas at 15:08, the flight – the 4th to be made by this particular New Shephard booster – lasted a total of 10 minutes 15 seconds. During this time the booster lifted the capsule, containing eight NASA experiments, to altitude before separating from it. The capsule went on to achieve a peak altitude of 105.6 km (66 miles), while the booster made a controlled descent, re-firing its engines to make an upright landing 8 minutes after launch.
After exposing the experiments to a brief period of weightlessness, the capsule also made its descent, deploying parachutes to slow itself and make a soft landing – much as it will when flights carrying up to 6 passengers and crew commence, possibly before the end of 2019.
Following the flight, Blue Origin also gave an update on progress with their much larger New Glenn 2-stage launch vehicle, designed to compete with SpaceX’s Falcon 9 / Falcon Heavy as a commercial launch vehicle. Standing 95 metres tall, the system will be capable of delivering 45 metric tonnes to low Earth orbit (LEO) and 13 metric tonnes to geostationary transfer orbit (GTO). These figures compare to Falcon 9’s 22.8 metric tonnes to LEO and a maximum of 8.3 metric tonnes to GTO and Falcon Heavy’s 63.8 metric tonnes (70.3 US tons) to LEO and 26.7 metric tonnes to GTO.
What is interesting about the update is that it shows New Glenn operating as a 2-stage vehicle with a large (7-metre / 23 ft) diameter payload fairing; originally, the 2-stage variant of the vehicle has been shown with a 5.4 m (17 ft) diameter payload fairing, the 7-metre fairing being seen as part of a larger 3-stage version of the rocket. This has fuelled speculation that the company has abandoned plans for a 3-stage vehicle.
Like SpaceX, Blue Origin plan to re-use the Blue Origin’s first stage, the booster being capable of making a controlled descent from altitude, then using its engines to make a powered landing – again in keeping with SpaceX – aboard a recovery ship at sea – in this case, a repurposed cargo vessel purchased from Sweden’s Stena Line .
The first flight of the New Glenn is scheduled for 2021.
SpaceX also hit a slight hiccup with its plans with its Starship Hopper test vehicle. Days after being announced as “complete”, and with hopes that the initial test flights could commence in just four weeks from the January 5th “completion”, the construction site was hit by high winds.
These winds, which peaked at 80 km/h (50 mph), snapped the mooring lines holding the vehicle upright, causing the vehicle’s nose cone to topple over and sustain damage.
Commenting on the situation, SpaceX CEO Elon Musk estimated that repairs would take “several weeks”, and the Hopper programme has likely been set back around eight weeks.