Category: Other Worlds and Tech

Venus has been the subject of a number of recent studies, one of the most intriguing of which suggests it’s runaway greenhouse effect was started by what might at first seem an unlikely candidate: Jupiter.

Our solar system is a place of mysteries, both in itself and in comparison with many exoplanet systems. While of the latter have Jupiter-size worlds, unlike our solar system, these tend to be found fairly close in to their parent planet (although there are some exceptions). It’s believed that these planets actually formed further out from their parent stars, but then migrated inwards under gravity, until a point of equilibrium / resonance was reached.

This idea of planetary migration has led to theories on how our own solar system may have developed early it its life, with one of them in particular being of interest here. Called the Grand Tack Hypothesis, it suggests that Jupiter likely  formed some 3.5 AU from the Sun (1 AU = the average distance separating the Earth from the Sun) – or about 1.5 AU closer to the Sun that its present orbit. During the initial evolution of the solar system, it gradually migrated closer to the Sun, perhaps getting as close as 1.5 AU –  a little further out from the Sun than the present orbit of Mars, before the combined gravities of the other outer planets – most notably Saturn – gradually teased it back outwards again, until that point of equilibrium / resonance was reached, leaving them all in the orbits we see today.

What is particularly interesting about the Grand Tack Hypothesis is that it accounts for a number of inconsistencies visible in the solar system today if it is assumed the planets all formed more-or-less in their current orbit sand never shifted very far from them. These can be summarised as:

• Why is Mars so small when compared to Earth and Venus? If the planets all formed within or close to their current orbits, then most models built around this idea result in Mars being of a comparable size to Earth.
• Why don’t we see a “super Earth” (or “mega Mars”) between the orbits of Earth and Jupiter? Again, models based on all the planets  forming in their present day orbits around the Sun indicate that there would have been sufficient accretion disk material in the region of Mars for a solid planet 1.5 times the mass of Earth (or greater) to have formed.
• Why is the asteroid belt so relatively uniform? Again, if Jupiter formed 5-5.5 AU from the Sun, then the material within the accretion disk should have resulted  not only in a Earth-size Mars, or a possible “mega Mars”, but should also have resulted in the formation of many more planetismals or “mini Marses” forming, smaller than Mars as weknow it today, but potentially somewhat larger than the likes of Vista and Ceres within the asteroid belt.

A migration of Jupiter towards the Sun accounts for the first two of these inconsistencies in much the same way: as it moved in towards the Sun, Jupiter both “ate” a lot of the material of the accretion disk sitting between the current orbits of Earth and Mars and also “pushed” some of it inwards, helping in the eventual formation of both Earth and Venus.

Then as it reversed course, it “ate” more of the debris, whilst pushing some of it away. Thus, the inward and outward movements of Jupiter left only sufficient material occupying the area of Mars’ orbit to accrete and form a relatively small rocky world. By the same measure, this pushing / absorbing of material within what would become the asteroid belt meant that material was much more widespread and unable to accrete sufficiently in order to create multiple “mini-Mars” planetismals.

But what does this have to do with starting the extreme greenhouse effect on Venus? The answer to this is quite complex.

In effect, Jupiter’s motion inwards not only pushed material towards the Sun that helped Earth and Venus to form, it also became sufficiently close to them both to encourage them into exaggerated elliptical orbits around the Sun, which at the time was somewhat cooler and dimmer than it has been for most of its adult life. Thus, Venus likely formed within what was then the Sun’s habitable zone, allowing an abundance of liquid water to form across the planet’s surface, whilst its elliptical orbit meant it experienced significant seasonal changes during the course of it’s “year”.

In particular, whilst “close” to the Sun, during its “summers”, the ocean-rich Venus would be subjected to greater amounts of evaporation of water from its oceans, which would in turn be subject to greater amounts of UV radiation. This radiation would split the water vapour into elemental oxygen and hydrogen, with the latter easily stripped away from the planet’s atmosphere by the solar wind, leaving the oxygen to combine with carbon to form carbon dioxide, generating what is called a “moist greenhouse” effect.

At the same time, the mass of water in the Venusian seas gave rise to a process called tidal dissipation which over time, gradually “dampened” Venus’ exaggerated orbit around the Sun, allowing it to be pulled into the kind of circular orbit it has today, eliminating the seasons whilst holding the planet closer to the Sun than it had been, further increasing temperatures and accelerating the moist greenhouse effect. This in turn would be aided but the Sun increasing in it radiative output, further accelerating the greenhouse effect as more and more water evaporated from the surface oceans, until the point of no return was reached.

A further result of the Sun’s increasing outflow of heat meant that its habitable zone was pushed outwards to encompass the Earth – but being that much further away from the Sun and under a greater influence of the gravities of the outer planets, Earth didn’t suffer either form that initial kick into a moist greenhouse effect, allowing it to maintain its seasons, and remain a more comfortably warm, wet planet.

It’s not 100% certain Jupiter’s migration was the kickerstarter for Venus’ greenhouse effect. There are, for example other mechanisms that may have dampened Venus’ orbital eccentricity without the influence of a massive planet like Jupiter – such as Milankovitch Cycles. But given the way the Grand Tack Hypothesis helps explain a good deal about the early solar system, it seem likely it may well have been responsible. And if it is correct, it has significant implications for any Venus analogues orbiting other stars and our understanding of the mechanisms at work in the development of exoplanets.

Continue reading “Space Sunday: Venus’ transformation, SLS and an asteroid” →

In late April, NASA awarded funding to develop human landing systems for the agency’s Artemis lunar programme to three commercial groups: SpaceX, Dynetics and the so-called “National Team” of Blue Origin, Lockheed Martin, Northrop Grumman and Draper.

All three are taking different routes to supply vehicles capable of landing humans on the surface of the Moon and then returning them to lunar orbit for onward transit to Earth. For the initial mission, which NASA has time-tabled for 2024 – a highly ambitious date – one of the three vehicles must be capable of delivering a crew of two to the south polar regions of the Moon and then back to orbit.

On August 20th, 2020, the National Team delivered a full engineering mock-up of its proposal lander / ascent vehicle to NASA’s Johnson Space Centre (JSC).

For those familiar with the Apollo lunar lander, the National Team’s vehicle is a veritable monster, standing over 12 metres (40 ft) in height. It comprises three elements: a descent element that physically lands on the Moon and that is topped by the ascent element, both of which are helped down to the lunar surface by a transfer element.

It’s a combination of vehicles that build on a definable heritage. The descent element is being designed by Blue Origin using the technology the company has been developing over the last three years for its automated lunar lander, Blue Moon.

The ascent stage, meanwhile, is being developed by Lockheed Martin leveraging technology used in NASA’s Orion Multi-Purpose Crew Vehicle (MPCV), the capsule vehicle that will be used to ferry crews to and from Lunar orbit. Finally, the transfer stage uses technology and elements from Northrop Grumman’s automated Cygnus resupply vehicle serving the International Space Station (ISS).

The newly delivered mock-up will remain at JSC through until early 2021. It will be used by NASA engineers and astronauts to ascertain how the vehicle works, what is required, and helping engineers within the National Team to validate the team’s approach to getting crew, equipment, supplies, and samples off and on the vehicle.

In all, the three contractors were awarded a total of US $967 million that would be used to meet the costs of the first 10 months in developing each of their proposals of a Human Landing System (HLS). Of the three, the National Team took the lion’s share of the funding, some US $579 million. As well as delivering the engineering mock-up to JSC, the National Team is also preparing for a certification baseline review of their proposed design, with NASA expected to release a draft of the call for proposals for the next phase of the programme in early September.

For their design, Dynetics is also working with Draper and with Sierra Nevada Corporation, the developers of the Dream Chaser space plane. Their design is the smallest of the three proposed HLS vehicles – and potentially the most flexible. It is effectively a two-stage craft comprising a core lander / ascent vehicle of a squat design, supported by “drop tank” units that provide fuel for the initial stages of descent to the lunar surface, and which are jettisoned as their supplies are used.

The core craft is designed to carry crew or cargo down to the surface of the Moon and return crews back to orbit to rendezvous with an Orion MPCV or the Lunar Gateway. In addition, the uncrewed cargo variant is designed so that once cargo has been unloaded, it can be utilised as an additional module for a lunar base, providing a means for the base to be routinely expanded.

SpaceX – a surprise receiver of funding for HLS – is proposing the use of a modified version of its Starship vehicle, one sans aerodynamic surfaces, as these will not be required for operations to / from the surface of the Moon.

It is expected that NASA will de-select one of the proposals in early 2021, allowing the remaining two to continue. However, there has been a crimp put in plans: NASA requested some US $3.3 billion specifically to fund the HLS programme in fiscal year 2021, but under the proposed House budget, only US $670 million is allocated to HLS development, and the Senate’s budget proposal may not significantly raise this.

Was the Sun Once Part of a Pair?

A theory published in the Astrophysical Journal Letters on August 18th, 2020, dips into the theory that the Sun was once part of a binary pair.

The theory itself isn’t new: the Sun was one of a number of stars formed around the same time in the “local cluster”, and so may well have been twinned with another early in its life, before the gravitational influences of other stars in the cluster forced them apart. In fact, in 2018, astronomers from the Instituto de Astrofísica e Ciências do Espaço in Portugal announced they may have discovered it in the form of star HD 186302, some 184 light-years away – although this has yet to be proven.

In the new publication, scientists from Harvard University point to the Oort cloud – a complex combination of a ring of icy planetesimals (the Hills Cloud) and a larger, more distant sphere of such objects, both of which lie beyond the heliosphere, as indicative that the Sun once had a companion.

Conventional thinking has it that the Oort cloud formed from debris left over from the formation of the solar system and its neighbours. However, models designed to show this have been unable to produce the expected ratio between scattered disk objects within the Hills cloud and outer Oort cloud objects. But if a relatively close stellar companion is introduced to the mix, modelling the formation of the Oort cloud elements and the distribution of objects within them becomes clearer, the paper’s authors claim.  Not only that: it may actually help explain how life on Earth started.

Oort cloud objects are rich in water ice and the minerals and chemicals essential to starting life. Having a stellar companion for the Sun dramatically increases the amount of perturbations that might ripple through the Oort cloud and send some of its objects to fall into the solar system – and potentially collide with Earth, bring that water and those compounds with them.

Continue reading “Space Sunday: the Sun’s twin, going to the Moon & SpaceX” →

Dream Chaser Cargo is an uncrewed version of Sierra Nevada Corporation’s (SNC) Dream Chaser space plane, and it is drawing closer to commencing operations ferrying supplies and experiments to and from the International Space Station (ISS), with operations due to start in mid-to-late 2021.

The world’s only non-capsule private orbital spacecraft, Dream Chaser Cargo is designed to be launched atop a United Launch Alliance Atlas V booster, and land like a conventional aircraft. Once operational, it will be capable of lifting some 900 kg of material within its cargo space, and a further 4,500 kg in a detachable and disposable module called Shooting Star that attaches to the rear of the space plane and includes a docking system for linking to the ISS, as well as supplying electrical power to the Dream Chaser.

Shooting Star can carry cargo both inside it, and in an external unpressurised unit. In addition, it can be used to hold some 3,500 kg of waste from the ISS, the module being jettisoned to burn-up in Earth’s atmosphere prior to Dream Chaser Cargo (which can also carry experiments back to Earth) making an atmospheric re-entry towards the end of a mission.

Now the first Dream Chaser vehicle has its wings and a name: Tenacity. The wings were delivered to SNC’s fabrication facility in spring 2020, and with work now cautiously resuming, the wings  – sans­ their outer skins – will be mounted on the vehicle’s air frame. During flight, the wings are folded against the fuselage so they can be contained within the payload fairings that protect the vehicle and its module during launch. After the fairings are jettisoned, the wings swing into their “flight” position so they can give Dream Chaser Cargo aerodynamic lift once back in Earth’s atmosphere.

Capable of fully automated flight, Dream Chaser Cargo has a significant advantage over the other ISS resupply vehicles capable of returning material to Earth – Dragon and Progress – in that it uses relatively “safe” fuels. This means ground crews can access the vehicle without having to wait for extensive safety checks to be completed, allowing delicate or time-sensitive cargo to be removed from the vehicle more quickly.

Betelgeuse’s Dimming: Explained But Still Mysterious

The orange giant Betelgeuse caused excitement in late 2019 / early 2020 when it went through a period of unprecedented dimming, even for a star as variable as it can at times be, its apparent magnitude (brightness as seen from Earth) reducing by a factor of 2.5 (or roughly 25-30%).

At the time, the dimming sparked speculation the star may have gone supernova, and we might be about to see the light of that event – it having taken some 700 years to reach us. Most astronomers doubted this was the case, and were confident the star would return to its more natural brightness, as indeed it did 2020 (see: Space Sunday: an exoplanet, a star and an asteroid).

Now, examinations of observations made by the Hubble Space Telescope (HST) in late 2019 suggest the star’s dimming was most likely caused by the ejection and cooling of dense hot gases. What’s more, additional observations suggest Betelgeuse may be going through another dimming period out-of sync with its usual cycles.

Between October and November 2019, HST observed dense, heated material moving outward through Betelgeuse’s extended atmosphere at 320,000 km/h, and it was following these observations that the more dramatic dimming of the star was seen from Earth, notably around the star’s southern hemisphere. It’s now believed that jet stream of hot gas reached a point millions of kilometres from the star and rapidly cooled to form a cloud of dust between the star and Earth-based observers, giving rise to the star’s apparent dimming.

However, study of the HST data revealed something surprising: the stream of ejected gas did not originate at the star’s rotational poles, as current stellar models would suggest. Rather, the Hubble data indicates that Betelgeuse can drive off material from any part of its surface. The data also revealed that during the event, the star lost a considerable amount of mass – around twice the “normal” amount it loses in a given period, just from its southern hemisphere. This in itself makes what happened to Betelgeuse unique: nothing like it has been previously seen in 150 years of observations.

Whether or not this means we’re seeing a new stage in Betelgeuse’s life cycle is unclear, but the mystery doesn’t end there. This is because data gathered by NASA’s Sun-orbiting Solar TErrestrial RElations (STEREO) satellite appear to suggest the star is again dimming, and outside of its more cycles. Until now, Betelgeuse has had two cycles of dimming and brightening. The first runs for around 25 years, the other runs through 425 days. Both coincided during the 2019/2020 dimming, contributing it. Thus for the star to be dimming now puts it well inside the 425 day cycle. Exactly what all this means isn’t exactly clear, but it has sparked considerable interest and observers will continue to monitor it through the rest of the year.

Quick Round-up

The last week saw the 2020 Perseids meteor shower reached its peak as the Earth passes through debris left by the comet Swift-Tuttle. As is usual, the event resulted in many outstanding photos, including the one below.

SpaceX

The next flight of the SpaceX Crew Dragon vehicle has been announced. Crew-1, the first “operational” flight will now targeted for October 23rd, 2020, when it well carry NASA astronauts Shannon Walker, Victor Oliver and Mike Hopkins, together with JAXA astronaut Soichi Noguchi as the nucleus of the Expedition 64 crew.

Originally scheduled for a late September / early October launch, the mission has been pushed back to allow additional time for the Russian Soyuz MS-17 mission to launch and rendezvous with the ISS.

After its 150m “hop”, Starship prototype SN5 has been rolled back for inspection and re-fit – possibly with the lengthened landing legs I mentioned in me previous space Sunday update. In the meantime, it appears that the next vehicle to make a test flight will be Starship prototype SN6. A further prototype, dubbed SN7.1, and comprising just a single fuel tank that uses new alloy end caps, is being prepared for a deliberate over-pressurisation test. This test vehicle has been dubbed SN7.1 in recognition of the SN7 tank section that was also tested to destruction earlier in the year.

However, most attention has turned towards prototype SN8, as it has been confirmed this will be the first of the prototype to be fitted with the upper section, nose cone and aerodynamic “wing” surfaces, and so will likely be used for the 20-km flight tests.

NASA

Whilst still 7 months from Mars, NASA’s Ingenuity helicopter drone, a part of the Mars 2020 mission and stowed under the Perseverance rover, had its batteries charged up to 35% capacity on August 7th, one week after launch. The 8 hour trickle-charge operation marked the first time the helicopter’s batteries have been charged in the space environment, allowing the vehicle to be powered-up.

The action was taken so that mission managers could check-out the drone’s electrical systems following launch and allow it to report on its overall status. The battery level will be maintained at the 35% charge level throughout the cruise phase, with routine re-charges, in order to allow the helicopter’s electronics to be warmed by a regular flow of electrical power.

On July 4, NASA’s Transiting Exoplanet Survey Satellite (TESS) finished its primary mission, imaging about 75% of the starry sky as part of a two-year-long survey. In capturing this giant mosaic, TESS has found 66 new exoplanets, or worlds beyond our solar system, as well as nearly 2,100 candidates astronomers are working to confirm.

During the first year of operations, TESS observed the southern sky, while in the second year, it turned its attention to the northern skies.  Allowing the way, the mission team has been able to introduce numerous improvements. Among other things, these now allow the satellite to capture a high-resolution image of the stars around us once every 10 minutes, three times faster than at the start of the mission, while it can now measure the comparative brightness of thousands of stares every 20 seconds, rather than every two minutes. These latter captures will more readily reveal changes in brightness that might be the result of a star “wobbling” in its spin due to the presence of planetary bodies (although TESS’s primary means of locating possible exoplanets is via the transit method) or the results of outbursts like coronal mass ejections (CMEs).

With the completion of its primary mission, TESS is into an extended mission, the first phase of which will run through until September 2020.

Virgin Galactic’s Supersonic Ambitions

As if flying tourists into space wasn’t enough, Virgin Galactic has announced it has entered into an agreement with Rolls Royce to build a new supersonic airliner aimed at the “premium” flight market.

The new aircraft – as yet unnamed – will, the company claim, fly some 50% faster than the Anglo-French Concorde, with a cruising speed of Mach 3 – allowing a crossing of the Atlantic in around 2 hours. If realised, the aircraft will cruise at an altitude of 18 km (60,000 ft) and will be capable of carrying up to 19 passengers.

Yes, that’s right. 19. The aircraft is intended to capture a modest percentage of the premium (business and first class) air travel market, with Virgin Galactic CEO Sir Richard Branson stating the company only need to capture 5% of that market to turn a profit. Currently, the aircraft has completed a “mission concept” review study involving Virgin Galactic, Rolls Royce (building of the engines that powered Concorde), aviation experts and NASA.

No details on when the aircraft might fly have been given, with the craft’s overall shape, size, dimensions, etc., yet to move out of conceptual drawings.