Did 'dark matter' or a star called Nemesis kill the dinosaurs?

December 11, 2015 by Konstantinos Dimopoulos, The Conversation
Credit: ESO/Y. Beletsky, CC BY-SA

The dinosaur extinction 66m years ago was most likely caused by a comet or big asteroid hitting the Earth. But given that asteroids don't actually hit our planet very often, could this really be the whole story? Many scientists are now asking whether some sort of cosmological event could have boosted the number of comets at the time, making such a collision more likely.

In a recent book, American cosmologist Lisa Randall suggests that a huge disk of "dark matter" – a type of invisible matter that is five times more common than "normal" matter – could have been responsible. When sweeping past our solar system such a disk would cause a tiny perturbation in space, amounting to a flicker in the that can knock comets out of the solar system's Kuiper belt or the Oort cloud just outside and send them towards the Earth.

But how credible is this theory? And are there other cosmological events that could explain the issue?

A tricky question

Mounting astrophysical and cosmological evidence suggests that there is a lot more dark matter in our galaxy than normal matter. Although it is invisible, we know it is there because of the gravitational pull it has on objects surrounding it.

The fact that it is dark simply means that it does not emit or absorb light, which makes it difficult to spot. Most cosmologists believe this matter, which is after all part of our galaxies and galaxy clusters, moves slowly, and is "cold" (because fast-moving particles are hot).

It’s behind you. Credit: Elenarts

Randall suggests that there's a whole disk of dark matter in our own galaxy. For it to have an effect on us it would need to be roughly aligned with the visible disk of the Milky Way so that the solar system oscillates around it as it travels around the galactic centre. But this is problematic because to be able to explain observations made so far, cosmologists believe dark matter would form large spherical halos around galaxies rather than disks.

To get around this, we need to make dark matter weirder than it already is. Randall suggests that there is more than one type of dark matter in the form of a "contamination", which she says could comprise 5-10% of the total dark matter. This kind of dark matter is different because it can interact with itself just like normal matter does. While the majority of dark matter can flow through itself without stopping, this special so-called "dissipative" dark matter can halt itself from moving and thereby form a galactic disk, like normal matter does. But, as Randall admits in her research papers, we do not know for sure that such dark matter would form a disk.

Even if it did, there is no reason why this dark disk should be aligned with the visible disk of the Milky Way, which it would have to do for it to unleash a huge comet towards the Earth.

Our nemesis

Randall is a world-renowned cosmologist, so her proposal is certainly credible. Provided that the model doesn't contradict future observations, Randall believes there is a small possibility in which her scenario would actually result in an increase in comets and asteroids.

So is there any evidence of this in the geological or palaeontological record? While the issue is still under debate, there is no conclusive evidence that extinctions have happened periodically. Randall's team claims the boost in comets may happen every 35m years or so, which some might argue could roughly correlate with mass extinctions.

So, despite a number of unknowns, is a dark disk the best cosmological proposal to explain mass extinctions? One other proposal that has been put forward is that the sun has a companion star, called Nemesis. Nemesis is a hypothetical, faint red/brown dwarf star orbiting the sun at a distance of about 1.5 light years. Every 25m years or so, it makes a pass closer to the sun, which could result in enhanced comet activity, because of its gravitational pull. This is not an unreasonable hypothesis, since the majority of stars belong to systems with multiple stars. However, brown dwarfs are relatively uncommon and Nemesis has not been observed (yet).

To me, Randall's scenario is more of an interesting "what-if" speculation than a realistic proposal. While her theoretical model is very thorough and more concrete than it may sound at first, the fact that there is no real evidence of periodicity in mass extinctions and crater formation on Earth is a problem. In addition, according to Occam's razor, which suggests the simplest solution is most likely the best, it is never a good idea to invent more types of than you actually need.

However, the proposal is certainly not impossible and should be taken into account when making observations. What's more, it serves to remind us that basic physics and cosmology are fundamental aspects of nature that may even influence the fate of life on Earth.

Explore further: Physicists suggest possible existence of other kinds of dark matter

Related Stories

Dark matter dominates in nearby dwarf galaxy

November 18, 2015

Dark matter is called "dark" for a good reason. Although they outnumber particles of regular matter by more than a factor of 10, particles of dark matter are elusive. Their existence is inferred by their gravitational influence ...

Recommended for you

China unveils 2020 Mars rover concept: report

August 24, 2016

China has unveiled illustrations of a Mars probe and rover it aims to send to the Red Planet at the end of the decade in a mission that faces "unprecedented" challenges, state media said on Wednesday.

Fossilized rivers suggest warm, wet ancient Mars

August 23, 2016

Extensive systems of fossilised riverbeds have been discovered on an ancient region of the Martian surface, supporting the idea that the now cold and dry Red Planet had a warm and wet climate about 4 billion years ago, according ...

Image: Planck's flame-filled view of the Polaris Flare

August 23, 2016

This image from ESA's Planck satellite appears to show something quite ethereal and fantastical: a sprite-like figure emerging from scorching flames and walking towards the left of the frame, its silhouette a blaze of warm-hued ...

11 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

vlaaing peerd
3.4 / 5 (7) Dec 11, 2015
I think proposing new forms of dark matter is not the way to go. Also just because she is reknown doesn't make this theory more credible, even I can see there's a lot of assuming in this story.

Also "given that asteroids don't actually hit our planet very often, could this really be the whole story?"

what's so aburdly extroardinary about a comet hitting our planet once every 60 million years, I have already witnessed a few passing by earth in my lifetime?

AFAIK, the most credible explanation is that our solar systems wobbles slightly in the galactic plane. This happens over a period of 30 million years which causes disturbances in the force (the Oort cloud) hence possibly causing a comet to get knocked towards the sun.
zorro6204
3 / 5 (9) Dec 11, 2015
Yeah, dark matter doing this or that, the fabled "nemesis", that would be big news, but the side effect of those effects wiggling one particular comet to end up on a path hitting the earth, who cares? All kinds of things could have caused that. Wrapping dark matter in with dinosaur extinction is just headline grabbing.
Torbjorn_Larsson_OM
4.1 / 5 (9) Dec 11, 2015
Alroy rejected periodicity in the fossil record by autocorrelation. And that should be the end of the story, since extraordinary claims need extraordinary evidence and the periodicity claim is so haphazardly (read: boringly) promoted in the face of evidence.

@vlaaing peerd: There is a difference between comets hitting Earth and comets large enough to cause mass extinctions. We know of only one such impactor - and not a comet, too - and it hit unluckily in modern sulfurous and calciferous sediments that did the deed.
yaridanjo
2.6 / 5 (5) Dec 11, 2015
Here are the orbital parameters for the half Jupiter mass ultra-tiny brown dwarf star.

http://www.barry....d.html#5

Here is verification of its period.

http://www.barry....d.html#8

Keep looking up.
Bigbangcon
3.2 / 5 (5) Dec 11, 2015
It is so nice to see that modern cosmology is finally diverting some of its attention from the far reaches of the cosmos to this humble planet earth. What else other than the tragic fate (it can or could be ours as well) of the giant dinosaurs should be the focus of such cosmic attention!
tblakely1357
2.6 / 5 (5) Dec 12, 2015
My vote is for aliens.
AGreatWhopper
2.2 / 5 (6) Dec 12, 2015
What a troll indulgent non-story. Among their basic cognitive dysfunctions is one that says that nothing is ever a coincidence. Coupled with an inability to appreciate scale, you get premises like the one at the start of this article. "That just seems too unlikely...so let's consider something MORE unlikely...because nothing is a coincidence".

QED: This is no longer a bona fide science site. Science is just the bait used to attract the trolls, which traffic and the revenue it generates is the reason for this site.
theon
5 / 5 (2) Dec 12, 2015
I'm so happy. I never knew what all this dark matter is good for. But now I know: to kick off the dino's and make space for us. Lucky me, that I got to know this!
cantdrive85
2.6 / 5 (5) Dec 12, 2015
Mounting astrophysical and cosmological evidence suggests
More like mounting misconceptions.
But this is problematic because...dark matter would form... rather than disks
No problem, let's contemplate some ad hocery;
we need to make dark matter weirder
Good idea!
one type of dark matter in the form of a "contamination", which she says could comprise 5-10%
Perfect, now there are flavors of dark matter.
this special dark matter can halt itself
Screw you Newton's 1st Law!

So far there seems to be a number of issues with this hypothesis, where's the cred?
Randall is a world-renowned cosmologist, so her proposal is certainly credible.

Certainly! This is awesome, popular scientists rock!
To me, Randall's scenario is more of an interesting "what-if" speculation
Whew, this guy was going nutjob for a minute there.
it is never a good idea to invent more types of dark matter than you actually need.
Oh the irony, it's monumental!
vlaaing peerd
not rated yet Dec 14, 2015

@vlaaing peerd: There is a difference between comets hitting Earth and comets large enough to cause mass extinctions. We know of only one such impactor - and not a comet, too - and it hit unluckily in modern sulfurous and calciferous sediments that did the deed.


I was talking about passing by earth (not hitting luckily), there have been more than a few near earth objects (NEO's) in the last 2 years that had a diameter larger than 2 kilometer, if such large rocks already pass by earth regularly, why do we have to come up with new forms of dark matter to explain a rock hitting us as if it were -such an anomylous event that we have to come up with the weirdest theory to explain it?

what I'm trying to say is:

1. a rock in that same order of magnitude hitting us once (in 65 million years) is not anomylous
2. coming up with new types of DM having to explain it, is just too much.
vicary
1 / 5 (2) Dec 15, 2015
It's funny how scientists follow an unconfirmed theory and even building theories upon that, this whole structure of hypothesis is too shaky, and it's not the way science works.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.