New spacey stories: killer asteroids, stellar DNA, and rogue planets

I meant to post at least once a month, but I think you’ll understand that it’s hard to find the time while juggling new freelance science writing work with a 9-month-old kiddo at home. Anyway, here’s a couple pieces I’ve published over the past month. Enjoy! (See links below for the full articles.) As usual, thanks go to my helpful editors: Heather D’Angelo, Lisa Grossman, Lauren Morello and Jane Lee.

 

Maybe Dark Matter Didn’t Kill the Dinosaurs after All

Artist’s impression of the Chicxulub impact. Credit: Donald E. Davis, via Wikimedia Commons

A giant asteroid or comet the size of a city smashed into the Yucatán 66 million years ago, likely causing the demise of dinosaurs and many other species. Scientists have wondered: is that a random, unfortunate event, or has life on Earth been subjected to periodic impacts from outer space?

Some researchers proposed that, if the dinosaur extinction — the last of five mass extinctions — had an astronomical origin, rather than being driven by volcano eruptions or global warming, for example, then maybe others did too. And if impacts from huge boulders of rock and ice drove these extinctions, they had to come from somewhere. It’s possible that dark matter could periodically dislodge distant comets from their tenuous orbits beyond Pluto, sending a few of them dangerously in Earth’s direction — thus linking the fates of dark matter and dinosaurs.

But a new study by a team of physicists and geologists from Durham University and Lancaster University in the United Kingdom appears to shoot down that dark matter interpretation. If it were true, extinctions would have happened in cycles. But these scientists pored over the fossil record over the past 500 million years, looking for extinctions occurring periodically, but they didn’t find any significant patterns like that in the data.

“We needn’t search the heavens to find reasons for these extinction events. The vast majority of them are due to Earth processes, not astronomical ones,” says David Harper, lead author of the study.

The dark matter idea, popularized by Lisa Randall’s 2015 book, “Dark Matter and the Dinosaurs,” might sound far-fetched. But…

[Read the entire story in Now.space, published on 14 March 2017.]

 

Family tree of stars helps reconstruct Milky Way’s formation

The red dwarf doesn’t fall far from the tree. Astronomers are borrowing a technique from biology to build a family tree of the origins of stars.

A star’s chemical make-up can tell you a lot about where it came from. The universe’s first stars were mostly made of hydrogen and helium, and they fused those elements together into heavier ones. When massive stars explode as supernovae, they disperse the heavier elements they’ve built into space, where they become the building blocks of the next generation of stars. Stars born after many generations have heavier elements in greater abundance than do older ones.

“This process of ‘descent’ mirrors that of biological descent, even though biological evolution is driven by adaptation and survival, while chemical evolution is driven by mechanisms that lead to the death and birth of stars,” write Paula Jofré at the University of Cambridge and her colleagues.

Stars move around the galaxy’s spiral arms and disc, making it difficult to figure out where they came from. But if they were born in the same cluster, stars should have similar chemical signatures…

[Read the entire story in New Scientist, published on 20 February 2017.]

 

The hunt for rogue planets just got tougher

New analyses cut down the estimated number of planets unattached to a star by half.

Most planets live their lives tethered to the star that created them. But some renegade worlds wander across the Milky Way without a host. Two new analyses suggest that Jupiter-sized rogue planets are a lot less common than scientists thought. The Galaxy is likely home to around 100 billion of these planets, one study shows, instead of the 200 billion proposed in 2011.

Two teams of researchers presented their findings on 2 February at a conference in Pasadena, California: one based on a recent statistical analysis and the other on observations of more than 2,600 microlensing events. These occur when a planet passes between Earth and a distant star at just the right angle to — temporarily — act like a cosmic magnifying glass. It can briefly brighten the light from the star and provide researchers with information about the size of the ‘lens’, or planet, which might not reflect any light. This technique is currently the only way to spot these giant rogues.

Previous estimates of the number of free-floating planets stemmed from a 2011 analysis of ten microlensing events suggestive of renegade worlds1. The authors hypothesized that there could be as many as two rogue worlds for every main-sequence star — one of the most common categories, which includes the Sun.

The 2011 finding flew in the face of how many astronomers thought rogue planets formed. In a binary system where each star hosts its own planets, the gravitational force of one of the stars could disrupt the orbit of a planet and fling it out of the system. There could be similar effects in a crowded cluster of stars, where one star could eject its neighbour’s outer planet.

These and other scenarios could produce some free-floating planets, but probably not hundreds of billions of them…

[Read the entire story in Nature, published on 8 February 2017.]

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