limits of habitability lie,” says planetary scientist Martha Gilmore of Wesleyan University, co-author of the new paper. “If we’re thinking about the search for life beyond Earth, we have to be open to the possibility that some other planet might host life that’s not just Earth-like life.”
The paper, published in Astrobiology, outlines a number of ways in which Venus, Earth’s closest neighbor, has forced a rethinking of what makes a planet habitable. For example, scientists have long considered the “habitable zone” around a star to be the sweet spot where temperatures allow for the existence of liquid water. Venus, despite being at the edge of the sun’s habitable zone, is far too hot for liquid water.
This has made scientists take a closer look at “a new and broader definition of habitability,” says Michael Way, an astrophysicist at NASA’s Goddard Institute for Space Studies and lead author of the paper. “Venus is telling us that some of the gases that lead to a runaway greenhouse effect, or a thick atmosphere, can push a planet outside of the traditional habitable zone.”
Venus has also called into question the assumption that a rocky planet needs a magnetic field to protect its atmosphere from being stripped away by the solar wind, the stream of charged particles that flows from a star. Venus doesn’t have a magnetic field, yet it has retained an atmosphere much thicker than Earth’s. This revelation has “broadened our view of what it takes for a planet to maintain a stable atmosphere,” Way says.”Venus provides us with a unique perspective on planetary limitations,” explained Stephen Kane, a UC Riverside astrophysicist and the first author of the paper. The study, published in Nature Astronomy, brings together a wealth of information about both Earth and Venus. It highlights Venus as a reference point for scientists to gain insight into the conditions that prevent life on planets orbiting other stars. Although Venus has an atmosphere similar to a pressure cooker that would be lethal to humans, it shares some similarities with Earth, such as similar mass and radius. This proximity prompts the question of why Earth is habitable while Venus is not.The outcome of Venus is believed to have been caused by insolation flux, the amount of solar energy it receives. Many scientists attribute this to a runaway greenhouse effect that led to the planet’s ruin. According to Kane, Venus receives 191% of the solar energy that Earth gets, which is thought to be a contributing factor to its unique characteristics. However, the absence of a moon, which influences Earth’s tides and water levels, is also a significant difference between the two planets. More NASA missions to Venus could provide valuable insights into the unknown factors and further clarify the differences between Venus and Earth.Venus does not possess a noticeable magnetic field. This lack of a magnetic field may be connected to the size of its core,” Kane stated. “The size of the core also provides insight into how a planet regulates its temperature. The Earth has a mantle that circulates heat from its core. The inner workings of Venus remain a mystery.” The composition of a terrestrial planet’s interior also impacts its atmosphere. This is evident on Earth, where volcanic outgassing has greatly contributed to our atmosphere.
At the end of this decade, NASA has plans for twin missions to Venus, and Kane is involved in both projects. The DAVINCI mission aims to explore the acid-filled atmosphere of Venus and measure noble gases and other chemical elements.
“DAVINCI will gather data on the atmosphere from top to bottom, which will greatly contribute to the development of new climate models. This will also help in predicting similar atmospheres on other planets, including Earth, as we continue to increase CO2 emissions,” Kane explained.
The VERITAS mission, led by NASA’s Jet Propulsion Laboratory, will not land on the surface of Venus but will provide scientists with detailed 3D maps of the planet’s landscape. rnrnThe instructions will help determine if the planet has active plate tectonics or volcanoes. According to Kane, current maps of the planet are incomplete, making it difficult to understand the level of surface activity versus changes over time. Both types of information are necessary. Ultimately, the paper supports missions to Venus for two primary reasons. First, better data from Venus can help ensure accurate inferences about life on distant planets. Kane also notes the sobering aspect of the search for life elsewhere in the universe, emphasizing the need for thorough exploration.The goal is to gather data in the exoplanet’s own environment. “We won’t be physically going there, landing, or collecting direct measurements,” Kane explained. “If we believe there’s life on the surface of another planet, we may never realize if we’re mistaken, and we’d be imagining a planet with life that doesn’t actually exist. The only way to get it right is by thoroughly understanding the Earth-size planets we can visit, and Venus provides us with that opportunity.” Another important reason for studying Venus is that it can give us an idea of what Earth’s future might look like. “One of the main reasons for researching Venus is because of our responsibility as stewards of this planet, to protect it and keep it safe for future generations.”The author, Stephen R. Kane, expressed his hopes that studying the processes that shaped present-day Venus, especially if it had a more hospitable past that is now destroyed, can provide valuable lessons for Earth’s future. He emphasized the importance of understanding how and when such devastating changes can occur. The journal reference for this article is Stephen R. Kane and Paul K. Byrne’s “Venus as an Anchor Point for Planetary Habitability,” which was submitted to arXiv in 2024 with the DOI: 10.48550/arXiv.2403.08830.Here is the article in HTML format that needs to be paraphrased to make it easier to read and understand:
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