So last night the last of the UK’s coal-fired power stations was turned off for good. Ratcliffe-on-Soar is no longer generating electricity by burning coal.
Graph from https://grid.iamkate.com by @kate@fosstodon.org. Look at that coal line drop from a high in 2012 to nothing today, while the energy generated from wind has increased dramatically.
So what if we expanded this policy to cover the whole world?
The baseline scenario
The UK may be the first G7 country to remove coal from our energy mix, but what if every other country adopted the same policy?
First, let’s look at the baseline scenario. This is what the state of the world might be if societal and technological changes were to continue at their current rate of progress with no policy changes.
Here is the energy mix going out to 2100.
En-ROADS baseline scenario showing the energy mix. In 2024, the majority of the world’s energy comes from a mix of coal, oil and gas – fossil fuels. As we move towards 2100, coal, oil and gas remain fairly steady, but the proportion of our energy from renewables increases steadily. Total energy use rises.
And here is how greenhouse gas emissions change in that baseline scenario – assuming no policy changes are made.
In this scenario, we get a global temperature change of +3.3C by 2100. Scary.
En-ROADS baseline scenario showing the change in greenhouse gas net emissions from ~40 gigatons CO2 equivalent per year in the year 2000, out to ~70 gigatons CO2 equivalent per year by 2100.
Let’s make some changes
Using the En-ROADS Simulator you can make a lot of changes. You can move sliders, you can fine-tune settings, and you can even change the underlying assumptions. It’s hugely flexible and you can simulate all sorts of possible policy interventions to see what impact they might have.
Let’s change settings to do with coal to simulate the whole world following the UK and stopping generating electricity using coal.
Here’s what the energy mix would look like.
Reducing coal causes it to disappear from the energy mix over a few years as infrastructure comes to the end of its life. By the mid-2030s there is no more electricity from coal.
What happens to that all-important measure of greenhouse gas net emissions? As we reduce coal use towards zero, greenhouse gas net emissions fall – because we are no longer burning as much coal.
Once coal disappears from the mix, the curve starts rising slowly again as energy demand continues to rise.
Importantly, the total CO2 in the atmosphere is reduced in this scenario. That’s a Good Thing.
In this scenario, greenhouse gas net emissions start to decrease over the next few years, before gradually rising again from the mid 2030s. From now on, the total emissions per year are lower than the baseline scenario.
Here’s what we changed in the model.
We’ve reduced new coal infrastructure completely, i.e no new infrastructure will be built to generate electricity from coal from now on. This policy is phased in over 10 years.
We’ve also reduced utilisation of coal processing plants and coal-fired power plants, completely ending coal utilisation as a fuel – also phased in over 10 years.
We also increase the annual retirement rate of coal plants used for electricity to 10%/year.
Coal primary energy demand reduces from 155 exajoules per year today, to zero exajoules per year by 2034. In the baseline scenario, the demand stays high and reaches more then 185 exajoules/year by 2100.
As a result you can see the coal primary energy demand (graph on the right) plummet to zero by 2034. Look at how the energy demand from coal drops to zero by 2034, compared with the baseline scenario.
Co-benefits
It’s not just about greenhouse gas emissions, although those are hugely important. When you make changes that reduce emissions, you get other benefits as a result.
What sort of results do we get?
Firstly, a reduction in the global temperature rise. The baseline model has a rise of 3.3C. Now we’ve reduced that to 2.9C. Not as far as we need to go, but it’s a start.
This comes about because of a change in the trajectory of the greenhouse gas concentration curve.
The baseline scenario has a concentration curve rising from just under 400 ppm to 800 ppm by 2100. In our scenario, this curve starts to rise less steeply, reaching 700 ppm by 2100 instead.
We also get other important co-benefits, things that have a positive impact on human health, the ecosystem, sea level rise, etc.
Here we can see how the removal of coal from the energy mix dramatically reduces air pollution from energy generation.
This graph shows a dramatic reduction in PM2.5 emissions, very small particles (2.5 micrometers or less in diameter) that can be easily inhaled and cause health problems.
PM2.5 emissions from energy generation go from between 20 and 25 megatons per year to less than 5 megatons per year by 2035 in this scenario, dramatically reducing air pollution.
This is great, right? Well, it’s a good step in the right direction, but it’s not The Solution.
Here’s the global sources of primary energy graph again. Notice what happens to the natural gas wedge (blue).
When coal use is reduced, demand for energy is still significant, so gas gets used to compensate. Unless there are also restrictions on gas, its demand will go up in response to expensive (or no) coal.
Notice how the gas wedge starts to grow once coal is removed from the mix.
How do we solve that? One solution is to tax (or restrict) the use of oil and gas as well. But that makes energy more expensive for everyone, and life more difficult for those who struggle to afford energy.
It’s a difficult problem. And as you can see here, although changing policy on the use of coal is a high-leverage solution, on its own it is far from the entire solution.
Getting closer to 2C
We need to keep coal, oil and gas in the ground for any solution to bring us close to 2C.
As the folks at Climate Interactive say “it takes many seed to plant a garden”. There is no one solution that is going to fix the climate. But removing coal from our energy production is a step in the right direction.
Want to explore further? Have a go at making your own scenario to bring the temperature rise to 2C or better? Go have a play with the simulator, and share your scenarios!
No, not Bonfire Night. We’re talking celestial firework displays! It’s October, and once again we’re coming up on the time for the annual Orionid meteor shower.
There’s been a trend over recent years of various parts of the media getting a bit hysterical about various astronomical phenomena, and in some cases hyping them up waaaaaay beyond any sensible justification and raising expectations to totally unrealistic levels. So if you’ve arrived here having heard stories about how spectacular the Orionids will be on October 21st, should you believe the hype? TLDR: no, but…
What is a meteor, anyway?
A meteor is actually quite mundane: a small piece of rock, generally smaller than a grain of rice that disintegrates as it flies through our upper atmosphere while travelling at many kilometres per second.
You can see meteors on any clear night of the year, all you have to do is find somewhere dark, look up, and be patient. These are called sporadic meteors and are just the detritus left over from the formation of the solar system, or debris from collisions between rocky bodies in the solar system. In the absence of something like a planet to crash into, they just float gently around in space not doing very much.
Usually you have to wait a while before you see a sporadic meteor, although because they are distributed randomly in space they don’t turn up a regular intervals and you may see a handful close together if you’re lucky.
Meteor showers, on the other hand, can be much more spectacular, and come round predictably at the same time each year. In the case of the Orionids, that time is October 21st – or thereabouts.
Origins of the Orionids
All meteor showers are the result of the Earth passing through regions of space with a higher than average concentration of these dust and rock particles. This happens because stuff gets left behind when comets (and some asteroids) go about their normal business on elliptical orbits around the Sun.
Comets are a bit like giant, dirty snowballs, containing large quantities of both ice, frozen gases, dust and rocks, and other volatile substances. We currently know of more than 3800 comets in the solar system, some of which we have actually visited giving us a much better idea of their chemical composition. Samples collected by the Stardust mission even finding the presence of the amino acid glycine, one of the fundamental building blocks of all life as we know it.
Comets spend most of their lives in the far reaches of the solar system where conditions are very cold indeed. Since comet orbits are elliptical, and centred on the Sun, their orbits also take them into the inner solar system for some of the time.
As a comet approaches the inner solar system it get closer to the Sun and so absorbs more solar radiation, heating the nucleus and causing some of the ice to sublimate – that is it turns directly from a solid ice into a gaseous vapour. As the ice turns to gas, the dust and rock particles embedded in it are released and float away, leaving a trail of debris behind the comet as it travels around the Sun.
When the path of the Earth happens to cross one of these debris trails, we see an increase in meteors coming through our atmosphere. This is the origin of a meteor shower, and explains why they are regular with predictable dates of activity.
The Orionid meteor shower is the result of debris left behind by Halley’s comet, one of the most famous comets in our solar system. The comet only returns to our skies once every 76 years (and is not due back until 2061), but the Earth travels through the debris trail each year, giving us the regular Orionid shower in October, and also the less well-known Eta-Aquariid shower in April/May.
Variations
A given meteor shower may not have the same level of activity, year to year. Some years a shower might be fairly unimpressive, with peak rates of only a few per hour. Other years we might have a much larger spike in activity and see rates of several hundred an hour. Rarely we might see rates of more than 1000 per hour – rarely seen meteor storm.
Imagine an aeroplane passing through the sky on a sunny day, leaving a contrail behind it in the sky. If you sit and watch that trail, it slowly expands, becomes less dense, and eventually disappears. Comet debris trails are a little like that (although not as easy to see, being made up of tiny dark particles of rock!).
As that trail ages, it gets less well-confined, the particles move apart slowly. Each time the comet comes round on its orbit, it deposits a fresh trail of denser debris along its orbital path. Add in the fact that the gravitational influence of the likes of Jupiter (and any other planet the comet comes relatively close to) can alter the trajectory of the comet, and you start to get a sense of why the number of meteors we see varies from year to year as the Earth passes though denser or less dense parts of the debris trail.
Very clever folks (such as the IMCCE meteoroids and meteors group) take observational data on the number of meteors observed each year (collected by seasoned observers – and you can help!) and build models of the debris trails for each meteor shower, and use those to make predictions about the number of meteor showers we are likely to see the following year. They are usually pretty accurate, but sometimes we see unexpected spikes in rates that were not possible to predict from past data alone – so it’s always worth a look.
What to expect in 2023
This year we are expecting good observing conditions on the peak night of October 21st, with the Moon at 48% illumination but setting before midnight. The best time to observe will be after midnight when the Moon sets and the constellation of Orion will have risen – this is the location of the radiant of this shower, the location on the sky the meteors appear to come from, and what gives the shower its name.
Some showers are particularly spectacular with more than one a minute on average. We’re not expecting that this year for this shower, with predictions of around 20 or so per hour. However, any shower has the potential to be spectacular, so it’s always worth a look!
The best way to observe is to find somewhere away from street lighting, wrap up warm, and look up! Obviously, you also need clear skies, but don’t worry if October 21st is cloudy as the streams of debris that cause most meteor showers are wide enough to provide activity over more than one night. Catching meteors takes patience, but can be worth the effort, and can contribute to citizen science projects.
Clouded out? I expect a lot of us (here in the UK, anyway) will be, thanks to Storm Babet. You might have more luck in other parts of the world. The nice thing about the Orionids is that they are equatorial, meaning you can see them from both the northern and southern hemispheres.
In December we will see the return of the Geminid meteor shower with a predicted peak of ~150/hour! Much more spectacular! The Moon will also be favourable as it will be very close to the Sun and not up during most of the night, aiding dark sky conditions which help you see the fainter meteors.
So, if you miss out this weekend, make a note in your calendar of December 14th, and make sure you remember to take a look!
If you’ve looked at any astronomy-related news over the last few days, you’ll have spotted that a supernova has exploded in a nearby galaxy, and astronomers are getting excited about it. Supernovae are not uncommon (we discovered more than 2000 of them just last year), but some get astronomers more excited than others. Why is this one interesting? Read on.
We think of stars like the Sun as lasting forever. On human timescales, that’s ok since most of them have lifetimes of millions to billions of years – our own Sun has been shining for some five billion years, and probably has enough fuel to last another five billion or so. But they are transient things, like everything else in the Universe, just on timescales it is difficult for us mere mortals to grasp. Even astronomers struggle!
Stellar lifecycles
Stars are giant fusion reactors, fusing hydrogen in the core to make helium, and releasing energy in the process. It’s this energy release that powers the heat and light we get from the Sun, and what makes all the other stars shine. Stars continue this fusion process for as long as the conditions are right in the core. You need a lot of hydrogen under very high pressure and at very high temperatures. Eventually, the hydrogen runs out and a star starts to die.
The way a star ends its life depends very much on one parameter: its mass. The amount of stuff that makes up a star. It’s a simple parameter, but it determines an awful lot about a star’s properties, lifespan, colour, luminosity, end point, and much else. Most stars are mostly composed of hydrogen (~75%) and helium (~25%) with small amounts of other elements. Stars that have formed recently (in cosmic terms) have a greater proportion of these “other” elements, for reasons I’ll come to, but they are still mostly hydrogen and helium.
When a star runs out of hydrogen in the core, the fusion process slows down, reducing the amount of energy released per second. That energy, in the form of photons, keeps the star from collapsing under gravity for most of the star’s life. When the number of photons decreases, the star can no longer counteract the relentless pull of gravity, and it starts to contract. In science terminology, the star is no longer in hydrostatic equilibrium.
As the star begins to contract under gravity, the pressure in the core begins to rise, the temperature also goes up, and we get to the point where conditions in the core are extreme enough that the fusion of helium can begin. This process also releases energy (although not at the same rate) and stops the collapse for a time. There isn’t so much helium though, so the helium-fusing period of a star’s lifespan is relatively short. The shell of mainly hydrogen around this hotter core is now also hotter, and can start undergoing hydrogen fusion too. Again, it doesn’t last anywhere near as long as the original hydrogen burning phase – a phase we call the main sequence lifetime, and which makes up the longest part of any star’s lifetime.
For stars like the Sun, that’s almost it. The helium also runs out, the core starts to collapse again. As the outer layers expand and cool, the star becomes a red giant. The core continues to shrink, eventually becoming a hot, dense object known as a white dwarf. The outer layers eventually drift off to form a (poorly-named) planetary nebula, the white dwarf core slowly cools and fades away over billions of years.
But for stars greater than a certain mass (somewhere around eight times the mass of our own Sun) the end is much more dramatic. These stars continue the fusion process, with the core developing like the layers of an onion, with each progressive layer fusing heavier and heavier elements as they are produced by the layers above them, all the way across the periodic table, up to iron. Iron is interesting, as its the first element in the periodic table where you cannot release energy through fusing it to create a heavier element. To fuse iron, you have to add energy. There’s nowhere inside a star for that injection of energy to come from, so the fusion process stops.
If there’s no fusion in the core, there is nothing stopping the layers above collapsing under gravity. And that’s what happens. Catastrophically.
The outer layers start to fall as the source of photon pressure to keep them up diminishes, until the iron core collapses under its own weight*, resulting in energetic shockwaves that literally rip the star apart. This is what we call a core collapse supernova. The physics of this are fascinating, and the theoretical modelling has come a long way in recent years as computers have become more powerful. (Other types of supernova happen too, astronomers recently detected radio observations from a thermonuclear supernova for the first time, but that’s for another day.)
Now, supernovae are not rare events. As I mentioned at the top, we discovered over 2000 supernovae just in 2022, with many more than that identified as candidate supernovae. Many of these are discovered by automated surveys that scan the sky each night looking for new objects, or astronomical objects changing in brightness. But some are discovered by dedicated amateurs with good equipment and an excellent knowledge of the sky.
SN2023ixf
This supernova, SN2023ixf, was discovered by one well-known supernova hunter, Koichi Itagaki from Japan. He’s discovered quite a few over the years! It is located in one of the spiral arms of the galaxy M101, also known as the Pinwheel galaxy due to its appearance, and it is pretty gorgeous:
M101 or the Pinwheel Galaxy, as seen by Hubble. Credit: ESA/NASA/Hubble.
The galaxy is some 21 million light years away, so the light reaching us now (including the light from this explosion) left the galaxy 21 million years ago and has only just reached us. Looking out into space is looking back in time, we only ever see the Universe as it was in the past.
So, if we discover so many of them each year, why are astronomers excited about this one in particular? Well, for one simple reason: its proximity. While we discover a lot of supernovae, most galaxies are a lot further away than M101, so most supernovae are also much further away than this. The closer a supernova is, the more easily we can study them, and the more detail we can achieve with our observations. A nearby event means that our telescope have better resolution (our images have more detail in them) and we collect more photons (an event of the same brightness twice as far away will appear four times fainter).
This galaxy has also been host to several supernovae over the years. Since we’ve been watching, we’ve spotted at least five in M101, the most recent being SN2011fe discovered in (no surprise!) 2011.
What we know so far
SN2023ixf was first discovered on May 19th and is being observed by astronomers around the northern hemisphere, so what do we know so far?
It’s a core collapse supernova, having gone through the evolutionary stages described above. Estimates from early modelling suggest that the progenitor star might have been about 15 times more massive than the Sun before it exploded. It has been getting brighter, heading for a peak magnitude of around mag 10 – far too faint to be seen with the naked eye, you’ll need at least a 4-inch/20-cm aperture telescope (and some patience!) to spot it.
So what’s all the fuss? It may be close, but it’s just one of many hundreds of thousands – so what?
Supernovae are cosmologically important. That nuclear fusion process I described makes elements up to iron in the periodic table. To get anything heavier than that, you need even more extreme conditions than in the core of a massive star, and that’s where supernovae come in.
In a supernova explosion, the extreme conditions created in the shockwave and subsequent blast result in a rapid burst of nucleosynthesis, creating elements much heavier than iron, including many that are important to the creation of things like the computer you are using to read this!
All of those heavy elements, as well as the stuff up to iron created before the explosion itself, get thrown out into the surrounding gas that make up what astronomers call the interstellar medium. This process is called enrichment, adding heavy elements to a gas that is mostly made of hydrogen and helium.
Stars form from the interstellar medium. Over dense regions in the gas start to clump together, gravity increases and more material gets pulled in. Slowly, over hundreds of thousands to millions of years, the gas accumulates, the temperature goes up, the pressure in the centre increases, until you have a hot ball of gas where nuclear fusion can begin in the core – et voila, a star is born!
The gas around the core then goes on to form planets in many cases. If that gas cloud only contains hydrogen and helium, you only get gas giants forming. If the gas also contains heavy elements in sufficient quantities, produced in previous supernova explosions, then you get rocky planets forming too.
If you’ve ever heard Carl Sagan talk about us being made of star stuff, this is what he means. Much of the chemicals that make life possible, that make up the crust the Earth, that make up you and me, and our computers, were made inside massive stars and released into space in supernova explosions.
Don’t panic?
Our own galaxy, the Milky Way, is also forming stars, some of which are massive enough to go supernovae in this way. We actually haven’t had one in the Milky Way since 1604 so we’re rather overdue for one.
Some stars we know of are big enough to explode this way. Betelgeuse is a red giant that has got astronomers very excited in the last couple of years by behaving in a way that could signal its impending doom. It hasn’t exploded yet, but keep an eye on it.
If a supernova did explode in the Milky Way it would likely appear extremely bright due to its closeness. Astronomers would go bananas.
Supernovae are energetic explosions, generating blasts of neutrinos, as well as strong radiation across the electromagnetic spectrum – radio, infrared, visible, ultraviolet, X-rays, gamma rays. Any planets in the neighbourhood would get a good dose of radiation.
Don’t worry though, there are no stars in the vicinity of the Sun that are big enough to be a threat to life on Earth by going supernova. The supernova candidates are all far enough away to not be a threat. They would be pretty cool to watch though!
The early hours of January 27th 2023 saw the closest approach to Earth of asteroid 2023 BU. The fact that this particular space rock was only discovered on January 21st, just a week earlier, combined with it passing just 3,600 km from the surface of the Earth (0.03x the distance between the Earth and the Moon) got the media rather excited. It’s trajectory brought it closer to the Earth than orbit of our geostationary satellites, but still well above the 200-300 km of things like the International Space Station located in low Earth orbit. Given how far apart geostationary satellites are, our communications infrastructure was not in any significant danger (this time).
This particular asteroid was estimated to have a diameter of 4-8 metres and was travelling at a speed of around 9.3 kilometres per second as it passed by. This might sound big, but it’s tiny by asteroid standards. If it had hit the atmosphere, it would have most likely burnt up entirely, leaving only tiny fragments reaching the ground, if at all. For comparison, the rock that disintegrated over Chelyabinsk in 2013 was estimated to be 20 metres in diameter – that one exploded in the atmosphere, showering small chunks of debris over the town. Assuming a similar density to the Chelyabinsk rock, asteroid 2023 BU likely had a mass of less than 1,000 tonnes.
Animation showing the close approach of asteroid 2023 BU on January 27th 2023. Image credit: ESA.
The thing is with an asteroid passing this close to a much larger object, the encounter will change its future orbital trajectory. Prior to this encounter, observations show that this asteroid orbited the Sun every 359 days. Observations made after the encounter allowed experts to model its new orbit, finding that it now orbits the Sun every 425 days. It won’t be back at the Earth now until December 24th 2029 when it will be some 14 million km at closest approach. Nothing to worry about. In fact, they’ve modelled its position all the way to 2139. The closest it will pass to us in that time is 528 thousand km in January 26th 2066.
The thing is, this happens all the time. As of today, according to the IAU’s Minor Planet Center, there are 31,207 known near-Earth asteroids, 850 of which are larger than 1 kilometre in size, and 2,328 potentially hazardous asteroids. And we’re finding new ones all the time. Just this year (we’re still only in February) we’ve had at least eleven objects pass closer than the Moon, at least five of which were not discovered until after closest approach! Again, don’t panic, they’re all pretty small and would be highly unlikely to do any damage.
2023 CX1 entering the atmosphere on Feb 13th 2023. By Wokege.
One of these actually impacted the atmosphere. Asteroid 2023 CX1 was discovered less than seven hours before impact! Again, don’t panic, it was tiny, about 1 metre in diameter, and burned up as an impressive fireball somewhere over the English Channel / Northern France (above). You can see reports of sightings on the IMO fireball report catalogue. This was only the seventh impacting asteroid to be discovered before it actually hit the atmosphere. It’s still pretty difficult to find these things in advance.
If you want to look at the population characteristics, JPL’s Center for Near Earth Object Studies has some data and charts you can play with – I’ve included a couple below showing the discovery rate of NEOs, colour-coded by survey, and the size distribution.
Discovery rate of NEOs, colour-coded by survey, dated Jan 31st 2023. Credit: CNEOS.
The above plot shows the increase in discovery of near-Earth objects. The surveys that have discovered the most objects are the Catalina Sky Survey and Pan-STARRS, although many are still discovered by amateur astronomers – including 2023 BU and 2023CX1! This is one of the science goals of the Vera C. Rubin telescope‘s Legacy Survey of Space and Time (LSST), to make an inventory of the solar system.
Size distribution of NEOs discovered to date, dated Jan 31st 2023. Credit: CNEOS
This one shows the size distribution of NEOs discovered so far. As you can see, there are not many in the 1000+ metres category – luckily! Those are the ones most likely to cause us damage, but they are also the easiest to spot. The thing with space rocks is that they are rocks. Rocks are usually pretty dull looking, they are often dark colours and don’t reflect much light. That is a problem when your trying to find them with an optical telescope – they don’t reflect much light, so are pretty faint and therefore difficult to detect.
If you’re a keen astronomical observer and are looking for a project, here’s the Minor Planet Center’s list of NEOs needing confirmation. More observations are always welcome, helping to pin down asteroid orbits, and you don’t need sophisticated equipment to contribute.
Keep watching the skies – there will be more of these! But they will get harder to spot as we launch more and more satellites, and install more and more lights.
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.
After all the fun with the planetarium shows, a couple of us at UCLan hatched a plan to ask kids to help us design a new Space Badge for Alston Observatory. We get a lot of Cub and Scout groups visiting the Observatory, but far fewer groups of Brownies or Guides. Cubs and Scouts have Astronomer badges, and Brownies have a Space badge, but Guides don’t (sadly). But, everyoneloves a good badge for their backpack/camp blanket/whatever! So, we’re asking people between the ages of five and sixteen to get creative and help us design a new Space patch that we will get made up and give out to young visitors to our Observatory. Know someone creative in the right age group? Ask them to get their pencils out! Hurry though, entries close on October 31st.
Calling all space fans aged 5-16 years old!
Use your artistic skills to design a space badge – from stars to planets, telescopes to extra-terrestrial life, create your design to inspire future space explorers.
The winning designs will be given out to Alston Observatory visitors.
The winner will receive a £30 Amazon voucher and there are books for the runners-up.
Competition closes 31 October 2021.
Ask your parent / guardian to review the full T&C’s.
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These days, Macclesfield is a much more lively town than I remember from my childhood. One (large) reason for this is the Barnaby Festival, a volunteer-run town festival that fills the town with arts and music. This year had a bit of a twist: the theme was SPACE! In all the meanings of the word, not just astronomical. I had the great pleasure of helping to plan this year’s festival as part of the live events team, and it’s been amazing.
One of the events I ended up working on was the Deep Space Lab, a collection of displays, activities and talks in the town hall running all day on Saturday and Sunday June 18-19th. For two days (apart from when I ran out to play with the samba band in the parade!), I ran the live observing part of the Deep Space Lab. Over the weekend we used telescopes run by the brilliant people at LCOGT (in Hawaii and Siding Spring, Australia) to observe a selection of astronomical objects in real time, watching the images coming in direct from the telescope in real time. Despite the rather large cloud bank sitting over eastern Australia for pretty much the entire weekend, the weather in Hawaii wasn’t half bad and we got some pretty stunning images.
The best of the images from the weekend are shown below. Astronomical colour images are usually made up of separate grey-scale images taken through different narrow-band filters which only let through particular colours of light. Most of the images taken during the Deep Space Lab were through red, green and blue filters, resulting in full-colour images like the one you see below. Astronomy is all about understanding the physics (and chemistry) of the universe using just the photons that reach us on the Earth – that is all the information we have, just the photons, so the more of them we collect, across as much of the spectrum as possible, the better we can understand what’s going on out there in all those stellar clusters, star-forming regions, and galaxies that we see. I don’t know about you, but I find it amazing how much we do understand about the universe from collecting those tiny photons.
Lagoon nebula, taken with an LCOGT telescope in Hawaii during Macclesfield’s Barnaby Festival 2016
M13, Milky Way globular cluster, taken with an LCOGT telescope in Hawaii during Macclesfield’s Barnaby Festival 2016
NGC5371, spiral galaxy, taken with an LCOGT telescope in Hawaii during Macclesfield’s Barnaby Festival 2016
M11, the Wild Duck cluster, Milky Way open cluster, taken with an LCOGT telescope in Hawaii during Macclesfield’s Barnaby Festival 2016
NGC6712, Milky Way stellar cluster, taken with an LCOGT telescope in Hawaii during Macclesfield’s Barnaby Festival 2016
CRL2688, Milky Way post-AGB star, taken with an LCOGT telescope in Hawaii during Macclesfield’s Barnaby Festival 2016
