Life on our planet faces many threats. Cosmically speaking, the three biggest threats life on Earth faces, are solar flares an coronal mass ejections, Earth-crossing asteroids, and locate supernova events – the violent explosions of stars as they die.
Of these three, Earth-crossing asteroids tend to get the most attention, as they are regarded as the most immediate n terms of potential threat and what we can actually do to actually mitigate that threat if we’re given enough warning. Solar activity is a risk, but fortunately, when even at the peak of its cycle, our middle-aged Sun is rarely viciously violent, and when it does get angry, it’s rare that Earth is directly in the path of an lash-out – although as I noted in my previous Space Sunday article, we have recently come close.
Supernovas are also a mixed bag – we certainly can’t stop them, and if one occurs that is sufficiently violent and close enough to us, then we could be in a spot of bother no matter where we are in our orbit around the Sun. If close enough, supernovas of Type 1a or Type II could go so far as to be extinction level events (ELEs). Fortunately, in order to do so, such a supernova would have to occur in a fairly massive star that’s within a few hundred light years of us – and there are precious few of those. And if if one did explode as a supernova, that are all so far away, we’d see them long before we’d feel the effects.
Take Betelgeuse for example, a star that has caused much speculation among some due to its recent behaviour. Even if we witness the light of its supernova explosion tomorrow, it would be another 100,000 years for the “hard” radiation of the explosion’s cosmic rays to reach us.
But what of smaller stars – white dwarfs – that are also given to going out with a supernova bang? There are a couple on our neighbourhood, but they are nowhere near that stage in their lives, nd by the time they are, we’ll pretty much be beyond the distance from them at which they could do us a mischief.
So, does that mean supernova are not a threat? No; leaving ELEs aside, a local supernova could still trigger long-term havoc with things like the Earth’s climate. In fact, a new study indirectly points to this possibly being the case around 2-3 million years ago, when the Earth was subjected to the effects of a nearby supernova.
The basic evidence for this comes from concentrations of 60Fe, an iron isotope, found in deep ocean sedimentary rock layers called the ferromanganese crusts. What is significant about this is that 60Fe doesn’t naturally occur here, but is a by-product of supernova events, thus leading some to conclude the remnants of such an explosion once washed over us. However, it has also been pointed out that 60Fe can also be synthesised by AGB stars as they approach the end of their lives without ever going supernova, so it is possible the deposits found on the ocean beds were purely the result of distant interaction with one or more AGB stars far back in the time of Earth’s youth.
Because of this ambiguity, a team from the Technical University of Munich gathered several dozen ferromanganese crust samples from four widely separated locations on the floor of the Pacific ocean and at depths of between 1.6 km and 5.1 km beneath the ocean surface. They subjected all of these samples to extensive analysis to see if they could find traces of other elements that could be tied to either a supernova or the output of an AGB star. And they were successful, finding concentrations of the manganese isotope 53Mn. This is significant as this isotope doesn’t naturally occur on Earth, nor is it a product of AGB stars – but it is a product of supernova explosions.
Further, the team’s analysis of both the 53Mn and 60Fe concentrations revealed that both are present in similar amounts and the same ratios throughout all of the samples studied. This suggests that both were present in the Earth’s biosphere at the same time, and were deposited on the ocean floor in similar quantities over the same period of time, again pointing to them having a common origin in a supernova event. What’s more, because 60Fe has a half-live of 2.6 million years before it decays into nickel, said supernova could not have occurred more than about 2.5 million years ago.
In addition, the concentrations of both isotopes proved sufficient for the team to estimate the like size of the star the caused the supernova: between 11 and 25 times the size of our Sun. That’s of a sufficient size for the supernova to create what’s as called a “bubble” or “cavity” in space: a region that appears to be almost completely devoid of matter. Interestingly, for the last 7-10 million years, our solar system has been travelling through just such a “bubble”, called the Local Cavity. It is believed to have formed as a result of number of supernova events that occurred between 20 and 10 million years ago – which creates an interesting overlap with the idea of a supernova affecting Earth some 2.5 million years ago.
2.5 million years ago also marks the start of the of Pleistocene period, a time of considerable climate change that saw repeated cycle of ice ages that in turn saw dramatic shifts in the flora and fauna, with multiple mini extinction events, This cycle then repeated in the late Pleistocene through early Holocene (11,700 years ago), and the planet started to warm up again, leading to further cycles of extinction (notably those mammals that had developed to level in the cold, like the woolly mammoth).
What triggered that sudden cooling is unknown, but while the Munich study doesn’t point it it directly, it has been shown that severe interference by cosmic rays can cause dramatic shifts in climate, particularly towards the colder extremes. So again, the time link between that ancient supernova evidenced in the ferromanganese crusts of the seabed and rise of the ice ages of the Pleistocene is interesting.
Starship SN8 Set for Pressure Tests
The core hull of the SpaceX Starship prototype SN8 was moved to the test stand during the pas week to undergo tank pressure tests. Fitted with the aft aerodynamic flaps that will help the vehicle “skydive” through the atmosphere, but sans the upper section, nose cone and forward aerodynamic surfaces, and currently without motors, the core section was due to undergo a pressure test as this article was being written.
This test involves the tanks within the section being filled to operating pressures with inert liquid nitrogen. A hydraulic ram under the stand the exerts pressure on the base of the structure to simulate the stresses the three Raptor engines that power the vehicle will place on the structure in order to verify its fitness for flight.
Should this test be successful, SN8 will have the upper sections added, and its engines mounted. It will then go through further tests, including actual fuelling and a static firing of it motors. Once all these tests have been completed, the vehicle will be ready for its 15 km high “hop”, which is likely to take place before the end of the month.
At the same time as SN8 is undergoing its tests, prototype SN9 is also being readied for its first flight.