Astronomers uncover risks to planets that could host life

sc604 — Mon, 05 Aug 2024 14:10:39 +0000

̽��ֱ��discovery suggests that the intense UV radiation from these flares could significantly impact whether planets around red dwarf stars can be habitable.

“Few stars have been thought to generate enough UV radiation through flares to impact planet habitability. Our findings show that many more stars may have this capability,” said first author Vera Berger, who led the research while based at the ̽��ֱ�� of Hawai’i and who is now based at the ̽��ֱ�� of Cambridge.

Berger and her team used archival data from the GALEX space telescope to search for flares among 300,000 nearby stars. GALEX is a now-decommissioned NASA mission that simultaneously observed most of the sky at near-and far-UV wavelengths from 2003 to 2013. Using new computational techniques, the team mined insights from the data.

“Combining modern computer power with gigabytes of decades-old observations allowed us to search for flares on thousands and thousands of nearby stars,” said co-author Dr Michael Tucker from Ohio State ̽��ֱ��.

According to researchers, UV radiation from stellar flares can either erode planetary atmospheres, threatening their potential to support life, or contribute to the formation of RNA building blocks, which are essential for the creation of life.

̽��ֱ��study, published in the Monthly Notices of the Royal Astronomical Society, challenges existing models of stellar flares and exoplanet habitability, showing that far-UV emission from flares is on average three times more energetic than typically assumed, and can reach up to twelve times the expected energy levels.

“A change of three is the same as the difference in UV in the summer from Anchorage, Alaska to Honolulu, where unprotected skin can get a sunburn in less than 10 minutes,” said co-author Benjamin J. Shappee from the ̽��ֱ�� of Hawai’i.

̽��ֱ��exact cause of this stronger far-UV emission remains unclear. ̽��ֱ��team believes it might be that flare radiation is concentrated at specific wavelengths, indicating the presence of atoms like carbon and nitrogen.

“This study has changed the picture of the environments around stars less massive than our Sun, which emit very little UV light outside of flares,” said co-author Jason Hinkle.

According to Berger, now a Churchill Scholar at Cambridge, more data from space telescopes is needed to study the UV light from stars, which is crucial for understanding the source of this emission.

“Our work puts a spotlight on the need for further exploration into the effects of stellar flares on exoplanetary environments,” said Berger. “Using space telescopes to obtain UV spectra of stars will be crucial for better understanding the origins of this emission.”

Reference:
Vera L Berger et al. ‘Stellar flares are far-ultraviolet luminous.’ Monthly Notices of the Royal Astronomical Society (2024). DOI: 10.1093/mnras/stae1648

Adapted from a ̽��ֱ�� of Hawai’i media release.

Astronomers have discovered that red dwarf stars can produce stellar flares that carry far-ultraviolet (far-UV) radiation levels much higher than previously believed.

Scott Wiessinger/NASA

A red dwarf star unleashes a series of powerful flares.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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New insights into the dynamics of past climate change

sc604 — Wed, 14 Oct 2015 07:05:16 +0000

A new study of the relationship between ocean currents and climate change has found that they are tightly linked, and that changes in the polar regions can affect the ocean and climate on the opposite side of the world within one to two hundred years, far quicker than previously thought.

̽��ֱ��study, by an international team of scientists led by the ̽��ֱ�� of Cambridge, examined how changes in ocean currents in the Atlantic Ocean were related to climate conditions in the northern hemisphere during the last ice age, by examining data from ice cores and fossilised plankton shells. It found that variations in ocean currents and abrupt climate events in the North Atlantic region were tightly linked in the past, and that changes in the polar regions affected the ocean circulation and climate on the opposite side of the world.

̽��ֱ��researchers determined that as large amounts of fresh water were emptied into the North Atlantic as icebergs broke off the North American and Eurasian ice sheets, the deep and shallow currents in the North Atlantic rapidly slowed down, which led to the formation of sea ice around Greenland and the subsequent cooling of the Northern Hemisphere. It also strongly affected conditions in the South Atlantic within a matter of one to two hundred years. ̽��ֱ��results, published in the journal Nature Geoscience, show how climate events in the Northern Hemisphere were tightly coupled with changes in the strength of deep ocean currents in the Atlantic Ocean, and how that may have affected conditions across the globe.

During the last ice age, which took place from 70,000 to 19,000 years ago, the climate in the Northern Hemisphere toggled back and forth between warm and cold states roughly every 1000 to 6000 years. These events, known as Dansgaard-Oeschger events, were first identified in data from Greenland ice cores in the early 1990s, and had far-reaching impacts on the global climate.

̽��ֱ��ocean, which covers 70% of the planet, is a huge reservoir of carbon dioxide and heat. It stores about 60 times more carbon than the atmosphere, and can release or take up carbon on both short and long timescales. As changes happen in the polar regions, they are carried around the world by ocean currents, both at the surface and in the deep ocean. These currents are driven by winds, ocean temperature and salinity differences, and are efficient at distributing heat and carbon around the globe. Ocean currents therefore have a strong influence on whether regions of the world are warm (such as Europe) or whether they are not (such as Antarctica) as they modulate the effects of solar radiation. They also influence whether CO2 is stored in the ocean or the atmosphere, which is very important for global climate variability.

“Other studies have shown that the overturning circulation in the Atlantic has faced a slowdown during the last few decades,” said Dr Julia Gottschalk of Cambridge Department of Earth Sciences, the paper's lead author. “ ̽��ֱ��scientific community is only beginning to understand what it would mean for global climate should this trend continue, as predicted by some climate models.”

Analysing new data from marine sediment cores taken from the deep South Atlantic, between the southern tip of South America and the southern tip of Africa, the researchers discovered that during the last ice age, deep ocean currents in the South Atlantic varied essentially in unison with Greenland ice-core temperatures. “This implies that a very rapid transmission process must have operated, that linked rapid climate change around Greenland with the otherwise sluggish deep Atlantic Ocean circulation,” said Gottschalk, who is a Gates Cambridge Scholar. Best estimates of the delay between these two records suggest that the transmission happened within about 100 to 200 years.

Digging through metres of ocean mud from depths of 3,800 metres, the team studied the dissolution of fossil plankton shells that was closely linked to the chemical signature of different water masses. Water masses originating in the North Atlantic are less corrosive than water masses from the South Atlantic.

“Periods of very intense North Atlantic circulation and higher Northern Hemisphere temperatures increased the preservation of microfossils in the sediment cores, whereas those with slower circulation, when the study site was primarily influenced from the south, were linked with decreased carbonate ion concentrations at our core site which led to partial dissolution,” said co-author Dr Luke Skinner, also from Cambridge's Department of Earth Sciences.

To better understand the physical mechanisms of rapid ocean adjustment, the data was compared with a climate model simulation which covers the same period. “ ̽��ֱ��data of the model simulation was so close to the deep ocean sediment data, that we knew immediately, we were on the right track,” said co-author Dr Laurie Menviel from the ̽��ֱ�� of New South Wales, Australia, who conducted the model simulation.

̽��ֱ��timescales of these large-scale adjustments found in the palaeoceanographic data agree extremely well with those predicted by the model. “Waves between layers of different density in the deep ocean are responsible for quickly transmitting signals from North to South. This is a paradigm shift in our understanding of how the ocean works,” said Axel Timmermann, Professor of Oceanography at the ̽��ֱ�� of Hawaii.

Although conditions at the end of the last ice age were very different to those of today, the findings could shed light on how changing conditions in the polar regions may affect ocean currents. However, much more research is needed in this area. ̽��ֱ��study's findings could help test and improve climate models that are run for both past and future conditions.

̽��ֱ��sediment cores were recovered by Dr Claire Waelbroeck and colleagues aboard the French research vessel Marion Dufresne.

̽��ֱ��research was supported by the Gates Cambridge Trust, the Natural Environmental Research Council of the UK, the Royal Society, the European Research Council, the Australian Research Council and the National Science Foundation of the United States of America.

Reference:
Gottschalk, J et. al. Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard-Oeschger events. Nature Geoscience (2015). DOI: 10.1038/ngeo2558

A new study finds that changing climate in the polar regions can affect conditions in the rest of the world far quicker than previously thought.

Other studies have shown that the overturning circulation in the Atlantic has faced a slowdown during the last few decades. ̽��ֱ��scientific community is only beginning to understand what it would mean for global climate should this trend continue, as predicted by some climate models

Julia Gottschalk

Left: Marine sediment core sample from the South Atlantic with fossilised partially dissolved shells of planktonic organisms. Right: Well-preserved plankton shells.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

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̽��ֱ�� of Cambridge - ̽��ֱ�� of Hawaii

Astronomers uncover risks to planets that could host life

New insights into the dynamics of past climate change