New Science with NuSTAR

25 October 2012
Presented by Ben Valsler, Dominic Ford.


How can we measure some of the most energetic events in the universe? This month, we're exploring the new science being carried out by NuSTAR, a space-based high-energy x-ray telescope. Plus, we'll find out why being outside the goldilocks zone might not mean there's no chance of life, as it seems other sources of heat may make even more planets and moons good places to look for biochemistry...

In this episode

- How the Moon was made

That the Earth's Moon owes its origins to a cosmic collision four-and-a-half billion years ago seems increasingly likely...

How the Moon was made

That the Earth's Moon owes its origins to a cosmic collision four-and-a-half billion years ago seems increasingly likely, according to new research announced this week.

The moonPrior to the Apollo missions of the 1970s, which retrieved samples from the lunar surface for analysis, the prevailing theory of the Moon's origins was that material had somehow "spun off" the early Earth and coalesced in orbit.

But analysis of lunar rocks shows that the composition differs subtley from the Earth's crust material, ruling out Earth as the sole origin.

This spawned a theory known colloquially as "the big splat", which advanced the idea that, early in its history, the Earth collided with a smaller world, known as Theia, ejecting a mixture of the surface crust from the two bodies into orbit around the planet.

This material, scientists speculated, is what formed the Moon. But, if this were the case, the material the Moon is made from should differ chemically from the composition of the Earth, but it doesn't.

Now, three papers in the journal Nature, by German, Israeli, French and US scientists, have conducted simulations of the early solar system and also made highly precise and accurate measurements of the levels of different chemical forms known as isotopes to probe the origin and birthdate of the Moon in more detail.

Together, these data lend support for a lunar collision theory.

One of the papers looks at the relative abundances of three isotopes of oxygen, which can be used as a chemical fingerprint.

Structures formed in the same regions of the solar system have similar isotope profiles, and by comparing the material on the Earth and Moon, this is what they see, suggesting that the impactor that collided with the Earth to form the Moon came from our cosmic neighbourhood, rather than farther out in the solar system.

The second paper, by running simulations of the formation of the early solar system, considers the likelihood of the existence of a collision with an impactor on the scale of the notional Theia. The simulations suggest odds of about 20% of this happening, which is small but reasonable.

The third paper looks at a different question, which is what happened to the Moon and Earth subsequently.

According to prevailing theories of the solar system's evolution, both Earth and the Moon should have collected, after their formation, a veneer of material accrued through collisions with cosmic impactors. And because the Earth is larger, it should have picked up more of this material than the Moon, widening the gap in the chemical makeups of the two.

This is what researchers have now measured, picking up as they have tiny differences in the levels of the element tungsten between Moon and Earth rocks.

Together, the results show that it's plausible for a Mars-sized object to have formed in a similar region of space and subsequently collided and merged with the young Earth.

Debris ejected by the smash accreted into the Moon, and then both bodies were decorated by material raining down on them later from space.

X-Ray Astronomy and the Nuclear Spectroscopic Telescope Array
with Professor Andy Fabian, University of Cambridge

How long would a round trip to the centre of the galaxy and back take?

31:56 - Explaining Extra Infrared Emissions

There is a mystery surrounding the amount of infrared light that bathes the universe –the so called cosmic infrared background radiation. It’s been detected by a number of space based...

Explaining Extra Infrared Emissions

There is a mystery surrounding the amount of infrared light that bathes the universe -the so called cosmic infrared background radiation.  It's been detected by a number of space based telescopes, but with clusters of higher intensity than could be accounted for by all known galaxies.  Now, a paper in the journal Nature suggests that this glow may be coming from orphaned stars - hurled out of their parent galaxies, and now resident in the local Dark Matter Halo.

Previous research had suggested that the radiation may have come from faint, distant background sources, too far away to be distinguished by the telescopes, or from intermediate dwarf galaxies.  These two hypotheses would result in a different distribution of IR, but previous studies had been too small to analyse the grand structure.

Infra-red view of the solar systemWith this in mind, Edward Wright of the University of California, Los Angeles and colleagues looked at data from the Spitzer Deep, Wide-Field Survey collected between 2004 and 2008.  After correcting for local sources of IR, and masking out radiation from bright stars, they were able to measure the spatial variability over large areas.  Although their measurements showed some correlation with the distant-galaxy hypothesis, they found that neither hypothesis was enough to fit their measurements.

They now propose that the "extra" IR may be coming from intrahalo stars - stars that have been thrown from their parent galaxies in violent interactions and now reside in the dark matter halo surrounding each galaxy.

The authors state a number of future tests that are needed to further understand the contribution of intra-halo stars, and in a related News and Views Article, Andrea Ferrara from the Scuola Normale Superiore in Italy, states that "It will be interesting to see whether the authors' proposal stands up to scrutiny."  Ferrara adds that understanding the effect of intra-halo radiation will help us to study early galaxies as they undergo a process of reionisation in the so-called "dark ages" of galaxy formation - a poorly understood chapter in the history of the universe.

Going Underground - Extending the Habitable Zone
with Sean McMahon, University of Aberdeen


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