Tag: Astronomy

Once regarded as a planet that may harbour life, Venus – as we know it today – is a hellish place. Cursed with a runaway greenhouse effect, the surface temperatures (averaging 735 Kelvin or 462°C / 863°F) are hot enough to melt lead and mark it was the hottest planetary body in the solar system. The atmosphere is both a toxic cauldron so dense that it exerts a surface pressure 92 times greater than our own – the equivalent of being 900 m (3,000 ft) under water on Earth.

Venus is also unusual in other ways: it has a retrograde rotation (it spins on its axis in the opposite direction to Earth and most of the other planets), and it takes 243 terrestrial days to complete one rotation but only takes 224.7 days to complete an orbit of the Sun, making a “day” on Venus longer than a year.

Despite its hostile conditions, it has long been believed that Venus was at one time in its ancient past a far more hospitable world, potentially warm a wet, and spinning a lot faster on its axis (quite possibly in the same direction as the Earth spins). However, at some point  – so the accepted theories go – Venus experienced a massive impact, one sufficient enough to slow – and even reverse – its rotation and which also left it the broiling, hostile world we know today.

However, a new study involving the University of Bangor, Wales, the University of Washington and NASA, suggests not only did Venus once had a liquid water ocean, but that ocean may have actually been the catalyst that brought about the planet’s dramatic change.

To put it simply, tides act as a brake on a planet’s rotation because of the friction generated between tidal currents and the sea floor. On Earth, this results in the length of a day being shortened by about 20 seconds every million years. Given this. the team responsible for the  study investigated how such interactions might impact Venus. Using a numerical tidal model, the accepted belief that Venus once had a world-girdling ocean, and applying it to planetary rotational periods ranging from 243 to 64 sidereal Earth days, they calculated the tidal dissipation rates and associated tidal torque that would result from each variation in ocean depth and rotational period. Their work revealed that ocean tides on Venus would likely have been enough to slow the planet’s rotation it down by up to 72 terrestrial days every million years.

This might not sound a lot, but of the course of around 10-50 million years, it would have been enough to slow Venus’s rotation and bring it to how we see it today. In turn, this slowing of rotation would have accelerated the evaporation of an ocean waters on the sunward facing side of the planet, both increasing the atmospheric density and trapping more heat within the atmosphere, accelerating the planet’s greenhouse effect, in turn increasing the rate of ocean evaporation in what would have been a closed cycle. Add to that the planet’s known volcanism, and the team estimate that it would have taken around 100-120 million years to turn Venus into the planet we see today.

This work shows how important tides can be to remodel the rotation of a planet, even if that ocean only exists for a few 100 million years, and how key the tides are for making a planet habitable.

– study co-lead Dr. Mattias Green, University of Bangor

The study findings have potentially important implications for the study of extra solar planets, where many “Venus-like” worlds have already been found. From this work, astronomers have a model that could be applied to exoplanets located near the inner edge of their circumstellar habitable zones, helping to determine whether they might have at some point potentially have had liquid water oceans, and how those oceans may have affected their development.

Fly Your Name to Mars

Mid July through August 2020 will see NASA’s next rover mission launched to Mars, and as with a lot of their recent exploratory missions, NASA is giving members of the public the opportunity to have their names flown with the vehicle.

Between now and September 30th, 2019, NASA is inviting one million members of the public to submit their names and postal codes to Send Your Name (Mars 2020). These names will then be laser-etched onto a little chip roughly the size of a penny that will be mounted on the rover and carried to Mars. In return, successful applicants obtain a “boarding pass” similar to the one shown below, indicating their name will be flown on the mission.

The Mars 2020 rover is based on the same chassis and power system as used by the Mars Science Laboratory Curiosity rover. It will also use the same type of landing system, featuring a rocket-powered “skycrane” that will hover a few metres above the surface of Mars and then winch the rover down to the surface. However – and for the first time in the history of planetary exploration – Mars 2020 will have the ability to accurately re-target its landing point prior to committing to lower the rover, thus allowing it to avoid last-minute obstructions that might otherwise damage the rover or put it at risk.

Core to this capability is a instrument called the Lander Vision System (LVS), which has been undergoing tests in California’s Death Valley attached to a helicopter. LVS is designed to gather data on the terrain the lander is descending towards, analyse it to identify potential hazards and then feed the information to a guidance system called Terrain-Relative Navigation (TRN), which can then steer the landing system away from hazards, allowing the skycrane to winch the rover to the ground in a (hopefully) a safe location.

Mars 2020 is due to be launched between July 17th and August 5th 2020 to arrive on Mars at Jezero Crater on February 18th, 2021.

Continue reading “Space Sunday: Venus, Pluto, and a mini round-up” →

On May 9th 2019, and after a lot of speculation following an April tweet (see Space Sunday: asteroid impacts and private space flights), Blue Origin founder Jeff Bezos unveiled the next step in the company’s space aspirations: their Blue Moon lunar lander.

The vehicle has been in development for some three years, with precious few details being given until now, other than it was initially indicated it would be capable of delivering up to 4.5 tonnes of equipment and material to the Moon’s surface in support of human missions. However, the vehicle has apparently been through a number of design cycles, and the unveiling presented a massively capable machine which  – while it wasn’t openly stated at the May 9th event (but is indicated on the Blue Origin website) – could be used in support of NASA’s drive to return humans to the surface of the Moon by 2024.

Somewhat resembling the descent stage of the Apollo Lunar Excursion Module (LEM), Blue Moon has the capability to complete variable missions up to and including landing crews on the Moon’s surface and lifting them off again. In its “basic” form, the lander will be able to land 3.6 tonnes of cargo on the Moon, while a “stretch tank” version will be able to increase that deliverable payload to 6.5 tonnes.

This payload will be carried on the flat upper deck of the lander, which will also include a robot crane (or cranes) capable of lifting it down to the Moon’s surface. In addition, the lander has an internal payload bay designed to deliver small satellites into lunar orbit as a “bonus mission”.

The most interesting element of the vehicle is perhaps its propulsion / power system. Blue Moon will be powered by the company’s new BE-7 motor, which uses liquid hydrogen and liquid oxygen propellants rather than storable hypergolic fuels. This allows the motor to generate up to 10,000 lbs of thrust, whilst also being “deeply throttlable”. The initial version of the motor will undergo its first “hot fire” test in the summer of 2019.

While the offer better performance capabilities than hypergolic fuels, liquid propellants need to be held at low temperatures, otherwise they can start to “boil off” to a gaseous state if they start to get “warm” (this is why liquid fuelled rockets appear to “steam” on the launch pad: they are venting fuel that has turned to gas that needs to be released to avoid over-pressurising and rupturing tanks).

While Blue Origin believe the exceptional low temperatures of the 2-week lunar night will help keep the lander’s fuel stocks cold and liquid, Blue Moon will still need refrigeration / insulation to prevent undue boil-off of the propellant stocks, which will add some weight to the vehicle. However, Blue Origin sees some boil-off of the liquid hydrogen ad advantageous: they plan to use boiled-off gaseous liquid hydrogen to help keep the liquid oxygen cold in its tanks and also as feedstock for the power cells that will be used to provide electrical power to the vehicle.

The latter are important again because of that 2-week lunar night. when there will be no sunlight to provide energy to any solar cells the vehicle might otherwise be equipped with to provide electrical power.

While initially intended to deliver science missions and payloads to the surface of the Moon in readiness for human landings. However, a future development with the vehicle could see it fitted with an upper stage crew / ascent module. Whether or not this might be used as part of NASA’s ambitions to met the goal of returning humans to the Moon by 2024 remains to be seen. However, Bezos has indicated Blur Origin is willing to help NASA to achieve this goal, and pointedly notes that that the company has a three-year headset in developing their lander when compared to others.

However, even outside of NASA’s plans, Blue Origin has its own hopes to send humans to the Moon. As I noted in my last Space Sunday report, the company’s April tweet about this announcement made an indirect reference to Shackleton Crater close to the Moon’s south pole. This is one of a number of craters believed to have water ice deposits within it, making it an ideal location for establishing a lunar base – and Blue Origin and Bezos have previously indicated it is their target for establishing a lunar base.

Lunar water ice is also another reason for the company opting to use liquid propellants with Blue Moon. Should their aspirations with Shackleton come to pass, then water ice – hydrogen and oxygen  – becomes a feedstock for refuelling Blue Moon landers once they are on the Moon, making them more efficiently reusable.

Blue Moon will be 7 metres (23 ft) across its payload platform, which will stand some 4m (14 ft) above the lunar surface on the basic lander. Fully loaded and fuelled, Blue Moon will weigh 15 tonnes at launch, but having burned the majority of its fuel during its flight and landing, will weigh only 3 tonnes after landing. By comparison, the Apollo LEM weighed 16.4 tonnes fully fuelled and stood 7.07 m tall, including the crewed ascent stage. Meanwhile, Lockheed Martin’s proposed lunar lander could be as much as 62 tonnes fully fuelled and stand 14 m (46 ft) tall.

Bezos declined to answer specifics on the vehicle such as when test flights are likely to commence, what will be the launch vehicle (although Blue Origin’s New Glenn would appear to be the most obvious choice), or how much overall development of the lander and its variants will cost. Doubtless, some of these details will become public in time.

Continue reading “Space Sunday: a Blue Moon, water worlds and moving house” →

I’ve written about the risk posed by the potential impact of a Near Earth Object on this planet several times within these Space Sunday articles. While they are rare, as we’ve seen with the Tunguska event of 1908, and the more recent  2013 Chelyabinsk air-blast and 2018 LA (ZLAF9B2) in June 2018, objects of a size sufficient enough to survive their initial entry into the Earth’s atmosphere before being ripped apart in a violent explosion can and do exist.

Nor is Earth alone in the threat – as witnessed by those observing the lunar eclipse of January 21st, 2019, the Moon can be hit as well. At 04:41 GMT, during the period of totality during that eclipse, numerous astronomers in North and South America and in Western Europe saw a sudden bright flash lasted less than 1/3 of a second. It was later attributed to an object around 30 to 60 centimetres (1 to 2 ft) across striking the Moon at around 61,000 km/h, producing a new crater somewhere between 10 and 15 metres (32 to 49 ft) across.

While the majority of the 10+ million objects thus far found crossing Earth’s orbit as they go around the Sun pose no real threat to us (in fact, the number of Potentially Hazardous Asteroids, or PHAs, has been put at just 2,000), and the risk of a substantial impact occurring in anyone’s individual lifetime is relatively remote, the fact is that – as Douglas Adams famously noted – space is big really big. Even the solar system is a vast place when compared to the size of Earth, big enough to hide any number of objects that might one day pose a very real threat to all life on Earth or, given humanity’s global distribution the potential to place one of our major cities at risk.

So how might we deal with such an eventuality? Currently, there are really only three practical options available to us – although others have been suggested, and more might be developed in the future. Which of them might be used depends on how much lead time we have in which to take action. To summarise:

• The gravity tug: if the impact is decades away, a spacecraft with a motor such as an electric ion drive could rendezvous with the asteroid and enter a halo orbit around it. The motor could then be fired along the axis of flight, allowing the gravitational influence of the vehicle to “pull” the asteroid onto a new course. However, this option can really only be used if the inclination of the threatening asteroid is relatively close to that of Earth’s; if the two are very disparate, the time needed to get the spacecraft to the asteroid using gravity assist manoeuvres around the Earth or Venus or even Jupiter, might simply be too long.

• The Kinetic intercept: this uses brute force to deflect the asteroid by slamming relatively solid masses into to, their momentum serving to shunt it into a slightly altered orbit around the Sun that is sufficient for it to miss the Earth.
• Nuclear deflection: similar to the kinetic intercept, but uses the shock waves of nuclear weapons detonated close to the asteroid to again shunt it into an altered orbit so it misses the Earth.

The major problem with the last two is the risk that if the asteroid is too fragile, rather than shunting it aside, they could shatter it, leaving Earth facing not s single object, but a scatter gun of debris, potentially with multiple elements large enough to devastate large areas of the planet’s surface should they enter the atmosphere and explosively disintegrate. This is also the reason why trying to directly blow an asteroid part using a nuclear strike isn’t regarded too favourably. There are other issues with each of these options that could also limit their effectiveness, or raise the need to repeat them, but they provide a general idea of how we might react.

Hence why the International Academy of Astronautics holds a Planetary Defence Conference every two years to discuss the latest findings with NEO and PHAs, and the ways and means to prevent such an impact – or at least the loss of life minimised. Since 2013, the 5-day conference has included a special “war game” type simulation to examine how a threat might be dealt with, and at the 2019 conference, held between April 29th and May 3rd, the simulation with publicly disseminated via social media as it progressed, to encourage grater public understanding about the need to better locate and track NEOs and PHAs (which are currently being discovered at the rate of around 700 a year).

In this simulation, which compressed an 8-year time frame into 5 days, the 200 astronomers, engineers, scientists and politicians at the conference were informed a large (fictional) asteroid around 300 metres across would slam into Colorado in 2027, unless then managed to divert it. Initially, things went well: a joint mission involving the USA, Russia, Europe, China and Japan used kinetic impacts to safely divert the bulk of the asteroid away from Earth. However, a 60m fragment broke away on a course that would see it hit the Earth’s atmosphere at 69,000 km/h (43,000 mph) and explode 15 km (9.3 mi) above Central Park, New York City. The force f the air blast would be sufficient to complete raze Manhattan and parts of New York City for a radius of 15 km (9.4 mi),  with the  effects of the blast felt up to 68 km (42.5 mi) from the epicentre. Plans were drawn up to try to deflect this fragment using a nuclear blast, but these became mired in political wrangling (not for the first time in these simulations)  until it was too late to achieve the desire deflection.

While such exercises might sound like scientists playing games, they do serve a purpose in that they help to underline the massive threat we face if we discover an asteroid is on a collision course with Earth – and the need for us to have better means to detect objects that might pose a threat early enough that we can take action, and also to better understand the processes – technical, scientific and political – that need to followed / overcome in order to prevent a collision.

They also highlight other issues as well. In this case, just how do you handle evacuating a city of 8 million souls? How much time is required (in the simulation, it came down to just 2 months)? What are the logistics required to ensure a (relatively) smooth evacuation? How and when should you tell the public? How do you avoid mass panic? This type of discussion is actually of major import, given current thinking is that if an object due to strike the Earth is 60 metres or less across, the focus should be on evacuating the area directly affected, rather than on trying to deflect it.

Continue reading “Space Sunday: asteroid impacts and private space flights” →

The black hole in the above image resides at the centre of Messier 87 (M87), around 16.4 million parsecs (53 million light-years) from Earth, and part of the Virgo galactic cluster of about 12,000 galaxies. It marks the first time we have directly imaged a black hole – and it is a remarkable achievement for a number of reasons.

Thanks to Hollywood, we’re all very probably familiar with the idea of black holes: a point is space where matter is so compressed that it creates a gravity field from which not even light can escape. However, black holes come in a variety of forms, of which the most unusual might well be those that exist at the centre of many galaxies – including our own. Referred to as “supermassive black holes” on account of their extreme mass, they on a scale many times larger than your typical stellar black hole (which, despite being referred to as “massive” – a reference to their gravitational attraction.

We don’t actually understand how galactic black holes like the one at the heart of M87 – and called M87*) formed, but being able to examine them directly could answer some fundamental questions about the nature of the universe and physics, as well as helping us to understand the role they play in the evolution of galaxies. The problem is, actually directly imaging any black hole is actually very hard simply because they are – well, black, and thus not the easiest of things to see against the blackness of space.

Fortunately, there is a way around this problem: black holes are not alone. Their massive gravity means they attract dust and gas, which forms an accretion disk around the black hole, spinning around them at enormous speeds and producing radiation in a range of wavelengths including radio, optical and infra-red. Given given the right capabilities, we can image a black hole against the radiation from this accretion disk.

But even with an accretion disk to shed light around a galactic black hole has its own set of issues. To image the one at the centre of our own galaxy, for example, is the equivalent of trying to stand in New York’s Times Square and being able to count the dimples on a golf ball 4,000 km (2,450 mi) away; and this despite the fact that the black hole at the centre of our galaxy is thought to be at least 60 million kilometres across.

Nor is trying to image them optically particularly helpful. They need to be imaged across a range of wavelengths – the problem here being that to do so, you need a radio telescope effectively the size of the Earth.

To achieve this, and following an idea first put forward 26 years ago by German radio-astronomer Heino Falcke, the idea of the Event Horizon Telescope (EHT) was developed. This involves linking numerous radio telescopes together so they can jointly examine a single target and gather data on it.

To image M87*, eight of the world’s most powerful radio telescopes and telescope arrays were linked together. Over a period of about a week in 2017, they were used to gather 4 petabytes of data about the light from M87* in the millimetre wavelength. The drives containing this data were then physically shipped from the observatories to the Haystack Observatory and the Max Planck Institute for Radio Astronomy, where they were plugged into a  grid computer made from about 800 CPUs linked through a 40 Gbit/s network, with the data processed by four independent teams using a series of tested algorithms to ascertain the reliability of the results. The final processing run was completed using the two most established algorithms to produce the image seen here.

This is in fact only the first galactic black hole image to b released. As well as studying M87*, the global EHT array has also gathered data on the black hole at the centre of our galaxy (and called Sagittarius A*), and at least two other supermassive black holes. However, imaging our own galactic black hole proved much harder, and delays in getting the physical hardware containing the data captured by the South Pole Telescope shipped from Antarctica to the Haystack Observatory has  meant that processing the data is still in progress.

According to theoretical physics – such as Einstein’s theory of relativity – scientists already knew what the image should look like: the aforementioned glowing accretion disk and the shadow of the black hole at its centre (so beloved of sci-fi films that feature black holes). However, simply seeing an image that matches what we believe we should be theoretically seeing helps further confirm Einstein’s theories about the nature of the universe around us.

From the actual image on M87*, scientists have already been able to confirm Einstein’s general theory of relativity under extreme conditions – notably the prediction of a dark shadow-like region, caused by gravitational bending and capture of light. They have also confirmed the shadow is consistent with expectations for that of a spinning Kerr black hole, which Einstein again predicted. Further, by combining the asymmetric nature of the accretion disk with the angle of the relativistic plasma jet created by M87* (not actually visible in the black hole image), astronomers believe M87* is spinning in a clockwise direction.

Further, the image has refined estimates of M87*’s size – 40 billion km across the event horizon (that’s 270 AU or 0.0042 light years; roughly 2.5 times smaller than the shadow circle shown in the image) – and its mass, estimated at 6.5 billion solar masses (± 0.7 billion).

We have taken the first picture of a black hole. This is an extraordinary scientific feat accomplished by a team of more than 200 researchers.

– Sheperd S. Doeleman, EHT project director

The image itself is shown in false colour to indicate the intensity of the emissions from the accretion disk. Yellow represents the most intense emissions, dropping to red as the lower intensity emissions, and black for little or no emissions. Were we able to see M87* with the naked eye, the colours would lightly be white, perhaps slightly tainted with blue or red. And while it has yet to be 100% confirmed, the colour bias towards yellow on the southern arc of the ring, together with its asymmetry, is thought to be the result of the gases in that region moving more in our general direction.

While this image has already revealed much, there are numerous questions we have yet to fathom. We may now know the nature of M87*, but we still don’t know how it was formed, or why so many galaxies have black holes at their centres. Nor do we as yet understand why some (like M87*) produce the great plumes of relativistic gas while others, such as the black hole at the centre of our galaxy do not.  So expect more to come as a result of studies arising from the work of EHT.

Continue reading “Space Sunday: black holes, Falcons and moonshots” →