Dr Megan Argo

Astrophysicist

Category: science

Nothing to see here – how satellites are ruining our shared skies

Have you ever camped somewhere quiet? Pitched your tent, carefully lit a small fire, watched the stars appear as the sky goes dark, picked up your phone to ask the internet if that’s Venus you can see – and then realised there’s no signal? With several private companies racing to develop the first operational space-based WiFi network, this could soon become a thing of the past – but so might your view of the stars.

Since the 1950s, humans have been launching satellites. From the early days of the space race the technology has developed dramatically, with satellites today carrying out tasks from communication to earth observation, measuring everything from ice coverage and wildfires, ocean currents and weather, to enabling the tracking of land use changes, predicting droughtsand spotting leaks from gas pipelines.

Arguably, the next logical step is a network of satellites providing global, universal internet access, and many companies are working on developing exactly this. These networks of satellites, known as constellations, will provide relatively cheap, low-latency and accessible internet to anyone on Earth. This will be particularly beneficial for remote locations where the potential benefits of internet access would be significant for human and economic development but cost of installing fibre is prohibitive.

Affordable, universal internet coverage enables fast, reliable communication, transcending socio-political boundaries, bridging the digital divide and helping people everywhere access education and reducing global inequality.

Is there space in space?

There is clearly huge potential, and lots to be gained. But is there enough room in low Earth orbit? According to data maintained by the UN Office for Outer Space Affairs, there are currently 8,221 satellites in Earth orbit, though less than half are operational. In total since the 1950s, humanity has launched more than 12,000 satellites into space. The number of objects launched in a year doubled between 2016 and 2017, and in 2021 alone we launched 1,800 objects. Including debris fragments, there are over 23,500 objects larger than 10 centimetres in size currently orbiting the Earth.  The accidental collision in December 2021 of the Chinese meteorological satellite, YunHai 1-02, with debris from a rocket launched in 1996 really hasn’t helped matters.  Neither did the Russian anti satellite test back in November that deliberately created a cloud of over 1,500 pieces of debris that threatened the International Space Station.

Space may be big, but the available space in Earth orbit is finite. Satellites have to avoid each other, they must communicate with other satellites in their networks and with those on the ground without interfering with each other, and we need to know accurately where they all are to avoid collisions. These are significant challenges; the safe use of Earth orbit requires cooperation.

Each of the companies developing these networks is planning and launching its own constellation, consisting of several hundred (and up to tens of thousands of) individual satellites. If we want to provide cheap, accessible internet to every community, then we will need to safely launch and operate many tens of thousands of satellites. How do we ensure this is done in a sustainable way?

The UN Committee on the Peaceful Uses of Outer Space produced guidelines on the sustainability of outer space activities, covering the avoidance of contamination (both of other planets and of the Earth), the safe re-entry of defunct satellites, sustainable use of the (finite) radio spectrum, the sharing of space weather and forecasting, among other things. However, these are guidelines, not laws, and are voluntary. Going forward, and in order to protect both the space around the Earth, the safety of the people on it and their view of the universe, we need international cooperation and agreement.

Blinded by the light

What about that view of the stars from our campsite? In good conditions we can see a total of around 10,000 stars with the naked eye, spread across both hemispheres. The darker your location, the more stars you can see. Over time our night skies have become brighter and brighter, with every new streetlight or security light making the stars harder to see. As a consequence, astronomical telescopes are confined to remote places, often on the tops of isolated mountain peaks.

However, this dramatic increase in satellite numbers now threatens these facilities and the science they enable. New constellations are launching at a time when several large, multi-country, expensive telescopes are under construction or becoming operational. The problem with the proliferation of satellites is that it becomes impossible to avoid them when trying to observe the universe. At least one of these companies is working with astronomers to try to minimise the effects on observations, but there is no regulatory compulsion to do so.  The big science questions these telescopes were built to address will become impossible to answer if we can no longer see the sky properly.

One telescope at risk is the Vera C. Rubin Observatory, a large optical telescope with a 3.2 gigapixel camera under construction in Chile, which aims to rapidly scan the sky to search for transient astronomical events and asteroids, among other things. This telescope should see first light this year, but will be particularly adversely affected by the extreme photobombing caused by large numbers of satellites passing through its large field of view.

It isn’t just optical telescopes that will suffer, either. For current and future radio telescopes, the proliferation of transmitters in orbit will make trying to observe the universe like trying to hear a violin over the sound of a jet engine. The cosmos will become as invisible to radio telescopes as the stars are to the human eye during the day.

Now, no astronomer is arguing against the human and economic benefits of universal internet (astronomy itself is being used as a basis for development projects around the world), but there is concern that this will ruin the view for everyone, and render much of modern astrophysics impossible in the long term. This ultimately leads to a waste of taxpayers’ money, a loss of training opportunities in the high-level technical and analytical skills that astronomy provides (most astronomy graduates do not become astronomers, but work in IT, business and the civil service, where they put those analytical skills to good use), and a loss of part of our shared cultural heritage.

One solution is obvious: we could just send all our telescopes into space. That’s fine if you have the money to do it, and it does happen (the Hubble Space Telescope and the James Webb Space Telescope being the best-known examples). In practice, this is always a more expensive option, it is a lot more risky, if something goes wrong it is difficult to fix, and you can’t build your telescopes as big for the same amount of money. This may be the long-term future of astronomy, but we are a long way from that being normal. It also does nothing for the view from our campsite.

Don’t look up?

For the moment, these constellations are being launched only with the go-ahead from country-based agencies (mainly in the US), but they impact the whole planet’s view of the universe. The night sky and the space around the Earth can (and, perhaps, should) be thought of as a natural wilderness and protected as such for everyone to enjoy and use, but that requires serious international cooperation and agreement – which, at present, does not exist.

Having internet access can drive economies forward and provide an excellent gateway to education. Is protecting the night sky for the minority of those who want to look at it (including amateur astronomers and children) more important than providing affordable internet in remote areas? Definitely not, but if we want to preserve the night sky for future generations, we need to act now. After all, if we can’t see the sky, we might not find the next incoming comet or asteroid until it’s too late.

[This article was originally published in Green World on July 7th 2020.  The numbers have been updated.]

OMG an ASTEROID the size of the EIFFEL TOWER!!!

You might have spotted the story in the media yesterday about an asteroid called Nereus which makes a close approach to the Earth today.  It’s described as the size of the Eiffel Tower and will zip past us pretty close, coming within 3.9 million kilometres.  Are we all doomed?  Of course not.  Here’s why.

Asteroid Nereus (or to give it its full designation, asteroid 4660 Nereus) is a lump of rock about 330 metres in diameter.  It was discovered in 1982, about a month after it passed within 4.1 million kilometres of the Earth.  It’s not spherical, more egg shaped, according to radar observations.  In late 2001/early 2002, astronomers used a radio telescope at Goldstone to send radio waves at the asteroid during one of its previous close approaches, using the reflected signals to measure its size and shape.  They found that it has dimensions of  510 by 330  by 241 metres, and it rotates on its own axis every 15 hours or so.

There are actually many thousands of lumps of rock this size in the inner solar system.  None of them are known to be on a direct collision course with the Earth, but we haven’t found all of them yet – not by a long way.  The current count of known asteroids is 1,113,527 (according to this NASA page), and this number is increasing all the time as we find more of them.  Some of these space rocks are large and easy to spot from Earth, but most are much smaller and are quite hard to find.

The problem with hunting for asteroids is that they are mostly (a) small, and (b) made of rock.  Small things reflect less sunlight, so they are fainter and need a bigger telescope to spot, and things made of rock tend not to be terribly reflective.  You’ve probably seen snow on mountains – the snow is much brighter than the rocky areas because white things reflect more sunlight than black/brown things.

Nereus is quite reflective for a rocky asteroid, but still tricky to spot because of its small size.  One estimate puts its maximum apparent magnitude (how bright it will appear to an observer on the Earth) at 12.6 which is pretty faint.  If you are lucky enough to live somewhere with dark skies, you can probably see stars an faint as about magnitude 6.  [This is one of those annoying astronomical measurements that doesn’t make intuitive sense – bigger numbers relate to fainter objects, so the Sun has an apparent magnitude of -26.74 while faint distant galaxies can have magnitudes of +20 or more.  The scale is also logarithmic as well, which  means that a difference of one magnitude is actually a factor of 2.5 in brightness.]  At its brightest, at closest approach, Nereus will be magnitude 12.6 which is more than 400 times fainter than the faintest stars you can see unaided.

Now, most of these floating space rocks are never likely to cause us a problem.  They orbit the Sun in the asteroid belt, a region between Mars and Jupiter where there is a concentration of asteroids.  Not all of them are in the asteroid belt though, many have elliptical orbits around the Sun, rather than the almost circular orbit of the Earth, and sometimes those orbits can bring an asteroid close to the Earth.   (The trick is to spot them coming!)

Nereus has an elliptical orbit within the inner solar system, taking 1.8 years to complete each orbit.  This orbit causes it to pass close to the Earth from time to time, but it also comes pretty close to Mars as well.  This actually makes it an excellent candidate for a sample return mission, and it was originally one of the candidates for the Hayabusa mission – but a delay meant that probe ended up visiting asteroid Itokawa instead.

OK, that’s the science background.  Should we worry about it coming so close?

Well, first some perspective.  At its closest on this occasion, Nereus will be 3.9 million kilometres from the Earth – that’s about ten times the distance between the Earth and the Moon.  Just on that count, we don’t really have anything to worry about.  This distance may be small when you compare it to the size of the entire solar system, but it’s still a long way.  Nereus will actually come even closer in the future; in 2060 its orbital path will bring it within 1.2 million kilometres of Earth.  That’s three times the Earth-Moon distance, so still not a threat.  If you are interested, here are the predictions for future encounters (including a close approach to Mars in 2089.

So no, we don’t need to worry.

I’ve talked about other asteroids though, and how the inner solar system contains an awful lot of them.  If we didn’t spot this one until it was already a month past a close approach, how easy might we miss another one that might come closer?  Well this is a risk.

In planetary terms, an asteroid impact could potentially do a lot of damage.  How much damage depends on the size of the impactor, the relative velocity of the asteroid and the Earth, and what the asteroid is made of.  There are lots of impact simulators around, but this one suggests that a collision with a 330-m object on land would result in a crater more than 4 km in diameter, and an earthquake of magnitude 7.8.  Their estimate is that an impact on this scale occurs on Earth (statistically) every 18,000 years.

There are plenty of efforts ongoing to find these asteroids and determine their orbits.  Many telescopes do this sort of work, and it’s something the Vera C. Rubin Observatory will be able to do really well (if the light from all the satellites being sent into low Earth orbit doesn’t cause too much of a problem… but that’s a topic for another day).

If we do find an asteroid that could impact the Earth, we need to have some way of dealing with it.  We can’t rely on Bruce Willis, so just last month NASA launched the DART mission to the binary asteroid system Didymos and its smaller companion Dimorphos.  The idea with DART is to test planetary defence techniques by, well, literally smashing a 500 kg projectile into Dimorphos at ~6.6 km/s (~15,000 mph) and watching how its orbital path changes.

The physics is simple (its just conservation of momentum) and, if all goes well, following the impact in October 2022 we should be able to observe a small change in the orbital period of Dimorphos.  It’s not the first time humans have visited as asteroid, and it’s not the first time we’ve deliberately bashed into one, but it is the first time we’ve actively tried to alter the trajectory of a solar system object.  If we do spot something dangerous headed our way, it makes sense to know how to make it less of a threat!

So, should we worry about Nereus?  No.  Categorically no.  It’s not a threat.  Should we worry about something we haven’t spotted yet hitting us in the future?  Well, it’s unlikely, but we really ought to be expending some resources to look.  It’s in our own interest as a species, after all.

Don’t have nightmares.

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