Category Archives: Space Sunday

Space Sunday: 100+ planets, taking a balloon to orbit, and budgets

A chart showing the to-scale sizes of two planets, 19 moons, 2 asteroids, and 87 trans-Neptunian objects, all of which could technically be considered planets orbiting our Sun. Credit: Emily Lakdawalla. Data from NASA / JPL, JHUAPL/SwRI, SSI, and UCLA / MPS / DLR / IDA, processed by Gordan Ugarkovic, Ted Stryk, Bjorn Jonsson, Roman Tkachenko, and Emily Lakdawalla

When is a planet not a planet – or more precisely, when should what is not regarded as a planet be a planet?

Right now, according to the International Astronomical Union (IAU), our solar system comprises eight formally recognised planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. That’s been the case since 2006, when the IAU opted to classify bodies orbiting the Sun in three ways:

  • As planets – defined as a) celestial bodies that (a) are in orbit around the sun; b) have  sufficient mass for their self-gravity to overcome rigid body forces so they assume a hydrostatic equilibrium (nearly round) shape; c) have cleared the neighbourhood around their orbit of other objects
  • As Dwarf planets – defined as celestial bodies which a) orbit the sun; b) have sufficient mass for their self-gravity to overcome rigid body forces to assume hydrostatic equilibrium (aka “is nearly round” in shape);  c) have not cleared the neighbourhood around their orbit; and d) is not a natural satellite
  • As Small Solar System bodies:  all other objects except satellites orbiting the Sun.

A composite image showing Pluto and Charon to scale to one another (but not at a scale separate from one another) using images returned by the New Horizons mission. Credit: NASA / John Hopkins University APL / SwRI

Thus, since 2006, Pluto has been a dwarf planet. However, moves are afoot to get things changed – and not just for Pluto.

In a paper authored by planetary scientists involved in the New Horizons mission which zipped through the Pluto system in July 2015, there is a call for the term “planet” to be redefined; if not by the IAU then at least in popular use. Should it happen, it could see the number of planets in the solar system leap from 8 to over 100.

The scientists argue that the IAU definition of “planet” focuses only on the intrinsic qualities of the body itself, rather than external factors such as its orbit or other objects around it. In fact, under the IAU’s definition, Earth, Mars, Jupiter and Neptune don’t actually qualify as “planets” as none meet the third criteria (c) – Earth, for example, has regular “close encounters” with asteroids which cross its orbit. Instead, the team offer a simpler definition:

A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has enough gravitation to be round due to hydrostatic equilibrium regardless of its orbital parameters.

Such a definition would mean that Pluto could regain its planetary status – as would the proto-planet (or small solar system body) Ceres, the dwarf planets of 136199 Eris (discovered in 2005, and the trigger-point for Pluto’s “downgrading”) , 136472 Makemake, and 136108 Haumea, together with (possibly) 50000 Quaoar, 90377 Sedna, 90482 Orcus and a host of trans-Neptunian objects tumbling around the Sun. Nor is that all; the new definition would also mean that the likes of  Jupiter’s Galilean moons, Saturn’s Titan and  Enceladus, Neptune’s Triton and many other bodies we regard as “moons” would be lifted to planetary status – including our own Moon.

A composite image using data gathered by the radar imager aboard NASA’s Cassini mission to Saturn to look through the normally opaque haze of Titan’s dense atmosphere to reveal its planet-like surface. Credit: NASA/JPL / University of Arizona

The paper proposing the change will be presented at the Lunar and Planetary Science Conference on March 20th to 24th, 2017 in Texas. And it has already come in for some criticism.

Mike Brown is the scientist largely behind Pluto’s demotion. Currently engaged in the search for the elusive “Planet Nine”, he (somewhat harshly) sees the efforts of the New Horizons team to get Pluto reclassified as being  about them wanting the prestige of having run a planetary mission, more than anything else.

However, there are valid reasons for seeking some kind of change, even if it is only informal. One is as basic as gaining more public interest in efforts to explore and understand the many environments found on planets and moons alike within our solar system.

“Every time I talk about this [the science and data gathered about Pluto by New Horizons] to the general public, the very next thing people say is ‘Pluto is not a planet any more’,” said Kirby Runyon, the lead author of the paper. “People’s interest in a body and exploring it seems tied to whether or not it has the name ‘planet’ labelled on it.”

How Pluto compares with other large Trans-Neptunian Objects, some of which also have their own moons. Earth and our moon can be seen at the bottom of the picture. Credit: Lexicon / Wikipedia, using NASA / Hubble Space Telescope data

There are scientific reasons for the definition to be broadened as well. Places like Pluto, Ceres, Europa, Io, Ganyemede, Callisto and Triton all evidence geophysical, hydrothermal, atmospheric and other characteristics very much in keeping with bodies such as Earth, Mars, and Venus. They are thus of exceptional interest to planetary scientists the world over. In fact, many of them (like Pluto) are completely re-writing our understanding of “planetary bodies”.

Ultimately, the team behind the paper aren’t going to put their proposal before the IAU for a change in the “official” definition of “planet”.  “As a geophysical definition, this does not fall under the domain of the IAU, Runyon notes, “[It]  is an alternate and parallel definition that can be used by different scientists. It is “official” without IAU approval, partly via usage.”

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Space Sunday: submarines, balloons and rockets

The four Galilean moons of Jupiter from volcanic Io (l) to distant Callisto (r). Europa and Ganymede (2nd and 3rd respectively) are thought to have liquid water oceans under their icy crusts, and each will be investigated by upcoming NASA (Europa) and European (Ganymede) missions. Callisto also may have a subsurface ocean, although it is thought to be more likely frozen or at least slushy ice. It will also be examined by the European mission

At the end of February / start of March 2017, NASA hosted the “Planetary Science Vision 2050 Workshop” at their headquarters in Washington, DC. The workshop covered a number of ideas for the future exploration of the solar system using automated means.

Two of the more interesting areas of discussion were the exploration of the “ocean worlds” of the solar system, notably Jupiter’s Europa and Saturn’s Enceladus. The other was options for exploring Saturn’s moon Titan.

The “Icy Worlds”

As I’ve recently reported Europa is already the target of the upcoming Europa Multi Flyby mission, due to launch in the early 2020, and which is now known once more by its earlier title of Europa Clipper. However, at the workshop, scientists looked at future options for exploring it,  starting with the lander mission already being planned as a follow-on mission.

What makes these icy worlds so interesting is that under their crusts of ice, there may well be oceans of liquid water. Europa and Enceladus in particular have demonstrated very strong signs that under a surface coating of ice, they have liquid water oceans, perhaps 100 km (62.5 mi) deep in the case of Europa.

Europa’s internal structure, showing the subsurface ocean which could be up to 100 km (62.5 mi) deep. This layer might also either be relatively solid ice or icy slush, depending on the amount of heat being generated deeper inside Europa

These oceans are kept in a liquid state due to gravitational flexing: they are constantly being pulled in different directions by the gravities of their parent planet and the other moons in orbit around it. The flexing generates heat, and this heat could be sufficient to keep the water trapped under the ice crust of such a world in a liquid state. It could also mean that the ocean bed of such a world might be the locations of hydrothermal vents and fumeroles which are pushing out the heat, energy, minerals and chemicals needed to kick-start life.

The reason Europa’s ocean might be liquid is flexing. The gravitational pull of Jupiter and from the other Galilean moons constantly plays on Europa, causing it to flex as it is pulled in different directions. This flexing generate heat deep inside the moon, and this heat could both radiate out to warm the waters of the ocean and give rise to hydrothermal vents of the sea bed, which could harbour basic life

Europa, Ganyemede and Callisto, around Jupiter show every indication of such sub-surface oceans, although Ganyemede’s and Callisto’s case, it might be more icy slush than liquid water. Both will be the subject of study by Europe’s Jupiter Icy Moons Explorer, due for launch in 2022.

Europa’s ocean is believed to be liquid both as a result of spectral analysis of the ice covering it, and because images of the moon captured by the Hubble Space Telescope appear to show huge geysers erupting from the moon’s south polar regions.

Geysers of water vapour have also been seen erupting from Enceladus by NASA’s Cassini mission, indicating it also has a liquid ocean under its covering of ice.

Worldlets like Ceres and Pluto also appear to have liquid interiors overlaying their cores, although the processes that might by allowing such liquid layers – likely water – have yet to be properly understood.

Of them all, Europa perhaps shows the strongest evidence for harbouring life-giving nutrients within its oceans, marking it as a prime candidate for study. This is because of the reddish-brown staining covering much of its surface. Most of this is likely debris from the huge volcanic eruptions which occur on Io, the innermost of the Galilean moons of Jupiter, and the one experiencing the greatest levels of gravitational flexing. However, some of Europa’s straining might be material deposited as a result of geyser action, particularly where the stains appear to run along many of the fault lines which crack Europa’s surface.

Given all this, planetary scientists are itching to get a vehicle onto the surface on Europa and – if possible, get one through the ice and into the ocean beneath it. Hence the discussions at the NASA workshop.

A dramatic line of plumes spray water ice and vapour from the south polar region of Saturn’s moon Enceladus as seen by the Cassini mission in February 2005. Similar venting of water may give rise to some of the brown stains of material covering much of Europa’s surface Credit: NASA/JPL / Space Science Institute

As I noted in writing about Europa Clipper (see the link above), a lander mission is already in the advanced planning stages thanks to strong support for missions to Europa in Congress. It could potentially take place just a couple of years after Europa Clipper arrives in orbit around Jupiter, and would have three mission objectives:

  • Search for biosignatures and signs of life by analysing the surface and subsurface deposits on Europa, particularly recently erupted material near the lander’s location
  • Analyse the composition of the surface ice and determine the proximity of liquid water beneath the ice
  • Attempt to identify the dynamic processes responsible for shaping Europa’s surface and its properties.

An artist’s impression of a possible Europa submersible, with it deployment system in the background. Credit: NASA

If the lander mission detects signs of life or strong evidence of life-giving materials within Europa’s ice sheet, then it will  likely pave the wave for the most ambitious mission of all: sending a vehicle to Europa with the means to penetrate the surface ice and release an automated submersible into the waters below to search for possible life.

While there is no time frame for such a mission, it has long been a goal for NASA and scientists. So much so that there have been numerous studies and even competitions for such vehicles, and a broad range of proposals and designs have been put forward. As such, it could be that such a mission could follow the Europa lander mission relatively quickly – perhaps within a decade.

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Space Sunday: Moon flights and the winds of Mars

The Dragon 2 crew capsule attached to its service module. Credit: SpaceX

The Dragon 2 crew capsule attached to its service module. Credit: SpaceX

While most private space tourism companies are busily going about various routes to offer sub-orbital flights to those who can afford them, Elon Musk’s SpaceX has stepped into the arena – and, as might be expected, made the bold announcement it will go one better: fly paying passengers around the Moon and back. And they plan to do it in 2018.

The announcement was made by Musk on Monday, February 27th during a press teleconference. If the flight goes ahead, it will allow two fare-paying passengers the opportunity to undertake a week-long journey out to and around the Moon, before returning to Earth. The flight would use a “free return” profile which would see it skim over the surface of the Moon and continue outward beyond it, possibly as far as 480,000 Km (300,000 mi) from the Earth (the average distance of the Moon from Earth is around 384,400km /  240,000 mi), before Lunar gravity takes over and hauls the vehicle back towards the Earth, where it would splash down.

It’s not clear how much the passengers would pay to be on the flight – but the going price for a seat aboard the Dragon 2 vehicle, which would be used for the flight, will be around US $58 million a pop to get to the International Space Station, once it enters service. It’s also far from clear if SpaceX can actually deliver on the goal of launching the flight in late 2018.

SapceX plan to use the Falcon Heavy as the launch vehicle for the lunar flight. When it enters service later in 2017, the Falcon Heavy will be the most powerful launch vehicle in the world today

SapceX plan to use the Falcon Heavy as the launch vehicle for the lunar flight. When it enters service later in 2017, the Falcon Heavy will be the most powerful launch vehicle in the world

In order to take place, the flight first and foremost needs a launch vehicle and a suitable space vehicle. SpaceX plan to use their mighty Falcon Heavy and – as noted – their new Dragon 2 crewed vehicle. There’s just a couple of problems with both.

The Falcon Heavy is not due to fly until some time later in 2017, and even then it will not be rated for crewed launches. For that to happen, it will have to be certified for crew use, and depending on how the initial flights go, that could take time. In terms of the Dragon 2, that is not scheduled to enter service until 2018 – and even then, its primary function is to fly crews to and from  the International Space Station (ISS).

Ferry flights to the ISS are vastly different to going out around the Moon and back. To start with, the outward flight from Earth to the ISS can be measured in just a couple of days – around a quarter of the time needed for the lunar trip.  The velocity (delta vee)  imparted to a spacecraft going to the ISS (28,000 km/h / 17,500 mph) is also a lot less than required to go to the Moon (40,000 km/h / 25,000 mph).

Elon Musk unveils a mock-up of the Dragon V2 capsule in May 2014. SpaceX now has their firs NASA contract to fly a crew to the ISS aboard the vehicle, probably in 2018

Elon Musk unveils a mock-up of the Dragon 2 capsule in May 2014.Credit: SpaceX

This means a returning Dragon 2 will be re-entering the Earth atmosphere a lot faster than the same craft coming back from the ISS, and will have to face much higher re-entry temperatures and a harsher deceleration regime. While the Dragon 2 can in theory do so, it is likely that significant testing on uncrewed vehicles will be required before the Federal Aviation Authority and NASA agree to any such flight taking place. On top of this, it will have to be demonstrated that the Dragon 2 can be outfitted for a deep space mission and keep a crew alive and well for around 7-8 days.

Given all this, there are widespread doubts the company can meet a 2018 deadline for such a mission – and SpaceX has tended to be ambitious with its time frames for achieve goals. They had originally slated 2013 as the year in which the Falcon Heavy would make its first flight – although in fairness, setbacks following the loss of two Falcon 9 vehicles also contributed to its launch being pushed back to 2017.

Red Dragon Delayed

As further evidence of SpaceX presenting time frames which are perhaps a little ambitious, on February 17th, the company announced its mission to land a variant of the Dragon 2 – dubbed Red Dragon – on Mars has been pushed back from 218 to 2020.

The aim of the mission so to fly an uncrewed 10-tonne Dragon 2 vehicle to Mars and land it safely. In doing so, the company hopes to gain valuable data on landing exceptionally heavy vehicles on Mars using purely propulsive means. This is because crewed landing vehicles on a Mars mission are liable to have a mass of at least 40 tonnes – far too much to be safely slowed in a descent through the thin Martian atmosphere by parachutes.

A SpaceX / NASA infographic outlining the Red Dragon mission - now slated for 2020

A SpaceX / NASA infographic outlining the Red Dragon mission – now slated for 2020

The planned mission would be undertaken entirely at the company’s own expense, although it would can science instruments and experiments supplied by NASA. For Musk it, and possibly three further Red Dragon mission which could follow it in the 2020-2024 time frame, is a vital precursor to greater ambitions for Mars.

As he outlined in September 2016 (see: Musk on Mars), Musk plans to start launching crewed missions to Mars, possibly before 2030. The initial missions will doubtless be modest in size in terms of crew and goals. However, his overall stated goal is to kick-start the colonisation of Mars. To do that, he plans to use vehicles massing at least 100 tonnes and which can make a propulsive landing on Mars. Whether he can succeed in even the step to land a crew on Mars  – and bring them back to Earth – remains to be seen. However, his Red Dragon mission is an important first step.

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Space Sunday: TRAPPIST-1, planet 9 and Europa

An artist's impression of the seven TRAPPIST planets, with -1b lower left and -1h lower right. The three planets in the star's habitable zone, -!e, -1f and -1g are the right-hand three in the top row. Credit: NASA

An artist’s impression of the seven TRAPPIST planets, with -1b lower left and -1h lower right. The three planets in the star’s habitable zone, -!e, -1f and -1g are the right-hand three in the top row. Credit: NASA

I recently wrote a space update special on the TRAPPIST-1 star system with its seven roughly Earth-sized planets. Since then, there has been speculation about whether any of them might support life, and what conditions for life might be like.

Whether life may have arisen on any of the worlds is tough question to answer. Three of the seven lie within the “habitable zone” where liquid water might exist (TRAPPIST-1e, -1f and -1g) – which is a positive for life as we know it. But for that liquid water to remain liquid, the planets must have an atmosphere. Currently, only TRAPPIST-1b and -1c have, through spectral analysis, been shown to harbour atmospheres, but these seem to be limited in scope, and could range from a water vapour rich atmosphere through to an environment similar to that of Venus.

On the negative side of the equation, the nature of their parent star, a super cool red dwarf with all internal action entirely convective in nature, means that all seven planets are likely subject to sufficient irradiation in the X-ray and extreme ultraviolet wavelengths to significantly alter their atmospheres, potentially rendering them unsuitable for life. Further, all seven are tidally locked, meaning they always keep the same face towards their parent star. This will inevitably give rise to extreme conditions, with one side of each world bathed in perpetual daylight and the other in perpetual, freezing darkness, resulting in extreme atmospheric movements and likely harsh weather.

Comparing the TRAPPIST-1 system with the solar system. Credit: European Southern Observatory / O. Furtak

Comparing the TRAPPIST-1 system with the solar system. Credit: European Southern Observatory / O. Furtak

Daylight on the planets would also be very different. Although one side of these worlds be forever in daytime, and despite the relative proximity with which they orbit their parent star, days on their surfaces would never be much brighter than sunset here on Earth, both in terms of colour and light intensity. This is because most of the light emitted by TRAPPIST-1 is radiated in the infra-red wavelengths, rather than visible wavelengths.

One the more positive side of the equation, despite the low levels of visible light, TRAPPIST-1 could still be able to sufficiently warm an atmospheres the planets might have, and the weather conditions might actually dissipate this warmth evenly over the planet’s surface, perhaps making it more hospitable to life.

It’s also likely the planets experience a lot of tidal flexing as they come under the influence of one another as well as their parent star. This flexing might give rise to hydrothermal and volcanic vents, which in turn could provide the necessary heat (energy), minerals and chemicals necessary to kick-start basic life.

Artist's impression of the three planets in TRAPPIST-1's habitable zone and to scale relative to one another. -1e (l) is the most likely to have extensive liquid water. It is 92% as big as Earth, with a mass of 62% that of Earth. It orbits its parent star about 10.8 times the distance from Earth to the Moon. -1f (c) is 1.04 times the size of Earth, but with only 62% of its mass. It is potentially water rich, and gets as much light from its star as Mars does from the Sun. -1g (r) is the outermost of the three

Artist’s impression of the three planets in TRAPPIST-1’s habitable zone and to scale relative to one another. -1e (l) is the most likely to have extensive liquid water. It is 92% as big as Earth, with a mass of 62% that of Earth. It orbits its parent star about 10.8 times the distance from Earth to the Moon. -1f (c) is 1.04 times the size of Earth, but also with  62% of its mass. It is potentially water rich, and gets as much light from its star as Mars does from the Sun. -1g (r) is the outermost of the three. It is 1.13 times Earth’s size with 1.34 times its mass. It is far enough away from its parent star that the surface is likely to be entirely frozen, but the gravitational influence of the other planets could give rise to a liquid water ocean under the ice. Credit: NASA

Studies of the TRAPPIST system will continue using the Spitzer and Hubble space telescopes and via ground-based observatories. However, as mentioned in my special report, it is likely to be the James Webb Space Telescope which will hopefully reveal many of the secrets of the TRAPPIST-1 system.

That said, and for those still wondering about intelligent life arising on any of these worlds, SETI, the Search for Extra-Terrestrial Intelligence has been “listening in” on the star for indications of radio traffic for some time (pre-dating the discovery of the first two planets in the system in 2016). Those surveys haven’t revealed any kind of radio emissions from the system that might be of artificial origin, but now we know there are seven planets, SETI has marked TRAPPIST-1 for further investigations with their Allen Telescope Array (ATA).

A Further Clue in the Hunt for Planet 9

Last year, Caltech astronomers Mike Brown and Konstantin Batygin found indirect evidence for the existence of a large planet in the outer reaches of our Solar System well beyond Pluto; since then, the search has been on. I first covered the hunt in January 2016, and followed it with updates in February 2016 and October 2016, and it now seems a new clue to the planet’s existence may have been revealed.

Planet X, if it exists,could equal Neptune in size, and orbits the Sun 200 times further away than Earth. Credit: Caltech / R. Hurt

Planet X, if it exists,could equal Neptune in size, and orbits the Sun 200 times further away than Earth. Credit: Caltech / R. Hurt

Astronomers using the Gran Telescopio CANARIAS (GTC) in the Canary Islands looked at two distant asteroids, called Extreme Trans Neptunian Objects (ETNOs). Spectroscopic observations 2004 VN112 and 2013 RF98 suggest that the two were once a binary asteroid pairing that were pulled apart as a result of the influence of a mass massive body between 10 and 20 Earth masses in size and about 300 to 600 AU from the Sun. As a result of this, the two bodies drew further and further apart over, time they became more and more separated to become how we see them today.

“The similar spectral gradients observed for the pair 2004 VN112 – 2013 RF98 suggests a common physical origin,” said Julia de León, an astrophysicist at the Instituto de Astrofísica de Canarias (IAC). “We are proposing the possibility that they were previously a binary asteroid which became unbound during an encounter with a more massive object.”

de León and his team carried out thousands of computer-based simulations to see how this might have happened, and found the most consistent result suggested the bodies were separated as a result of a close passage by a massive planetary object around 5-10 million years ago.

As it might be: estimates concerning Planet Nine's possible size, mass, etc., should it exist. Credit: Space.com / Karl Tate

As it might be: estimates concerning Planet Nine’s possible size, mass, etc., should it exist. Credit: Space.com / Karl Tate

What is particularly interesting here is that the location of the two asteroids, coupled with the suggested mass of the body which pulled them apart and the distance it is believed to have been from the Sun, also fit the broader parameters for where the orbit of Planet 9 might reside, and the estimated mass of the planet. Thus, when combined with the eccentric orbits of several Kuiper Belt Objects believed to have been perturbed in their orbits around the Sun by planet 9, it gives further credence to the idea it really is out there, somewhere.

When – and if – it might eventually be found is open to question. However, it is hoped that a  recently started “citizen scientist project will encourage amateur astronomers around the world to join in the hunt for Planet 9.

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