Some may find it poetic that the Sun from which Earth originated 4.5 billion years ago will likely consume the planet five billion years from now (Clery, 2023), as the star becomes a white dwarf.
The Zwicky Transient Facility, or ZTF, is a wide-field camera attached to the Samuel Oschin Telescope at the Palomar Observatory in California, United States (Kostadinova, 2022). In May 2020, the ZTF spotted a star approximately 12,000 light years away from Earth that bulged up to a million times its original size in ten days. This star was later named ZTF SLRN-2020. A nova occurs when one of two orbiting stars in a binary system becomes a white dwarf, which is a dying star that solely consists of its hot core. White dwarfs gravitationally attract their companion star’s hydrogen-rich outer atmospheres, causing nuclear explosions a thousand times brighter than the stars (Schaefer, et al., 2014). The observed phenomenon was first suspected to be a nova, but anomalous data from the telescopes at the W.M. Keck Observatory in Maunakea, Hawaiʻi prompted further investigation (McDermott-Murphy, 2023). While it is characteristic of novas to expel hot gases like hydrogen and helium, the data displayed the sole emission of molecules that exist at cold temperatures. Kishakay De, a graduate student at Caltech at the time, obtained infrared data from a Wide-Field Infrared Camera at NASA’s NEOWISE space telescope to investigate the cause of deviation (Clavin, 2023). The data associated with Star ZTF SLRN-2020 is contrasted with data previously collected on other red novas in Figure 1.
Figure 1: A graph that compares luminosity with outburst durations of various red novas. Contours show inferred ejecta mass in units of both solar and Jupiter mass on the left-hand side and magenta diagonal lines show outflow velocity on the right-hand side. This data reveals that the outburst of star ZTF SLRN-2020 had a luminosity and ejected mass that was 100-fold lower than any other known red nova. The velocity of the mass lost is an order of magnitude lower in comparison to outflow velocities in other novas as well (De, et al., 2023).
The observed differences in luminosity and outflow velocity between the ZTF SLRN-2020 explosion and other red novas in Figure 1 prompted scientists to hypothesize that the star had merged with an object that had 1/1000th of a star’s mass (Clery, 2023). The star was also detected brightening in infrared light, thus indicating the presence of dust and confirming the live observation of planetary engulfment for the first time in history. Hence, the initial flash observed by ZTF was concluded to be the star ZTF SLRN-2020 blowing off its outer layers to eliminate the energy transferred when swallowing a planet in its orbit whole. As the gas giant ten times the size of Jupiter disintegrated, the material that blew outward generated the cold dust that remained as long-lived infrared brightness for the following year (Clavin, 2023).
Nonetheless, the likelihood of Earth’s environment remaining habitable for human life to experience the planet’s destruction in five billion years is slim to none. Before engulfing Mercury, Venus, and Earth, scientists predict the Sun will increase in brightness by ten percent every billion years as it enlarges into a red giant and burns helium instead of hydrogen (Scudder, 2015). Increased heat from the Sun will cause more water to evaporate from the Earth’s surface and be held in the atmosphere to act as a greenhouse gas (GHG). With human activities like burning fuels and farming livestock excessively emitting GHGs as well, the combined accumulation of GHGs from both natural and human sources will expedite the process of evaporation. The Earth’s atmosphere will eventually lose all moisture, leaving the planet unsustainably hot, dry, and barren in one billion years (Scudder, 2015).
Just as human life did not exist for the first five billion years after Earth’s formation, it will likely cease to exist for the last five billion as well.
References
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Clery, D., 2023. A dying star consumes a planet, foreshadowing Earth’s fate. [online] Science. Available at: <https://doi.org/10.1126/science.adi5399> [Accessed 16 September 2023].
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Scudder, J., 2015. The Sun won’t die for 5 billion years, so why do humans have only 1 billion years left on Earth? [online] The Conversation. Available at: <https://theconversation.com/the-sun-wont-die-for-5-billion-years-so-why-do-humans-have-only-1-billion-years-left-on-earth-37379> [Accessed 20 September 2023].