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This decline was followed by a noticeable warming at the South Pole, an equally stunning finding.
These observations were made by an international team of astronomers who analyzed nearly 100 thermal infrared images of Neptune in an effort to piece together general trends in the eighth planet’s temperature from the Sun.
Thermal images of Neptune taken between 2006 and 2020
Photo: ESO/M. Roman, NAOJ/Subaru/COMICS
Neptune-101
- The diameter of the planet is 49,244 km, which is about four times that of Earth.
- Its temperature varies between -218 and -200°C.
- This planet is at a distance of 4.5 billion kilometers from the Sun (on average).
- It has 14 moons.
- Like Uranus, it is an ice giant. It is mainly composed of water, ammonia and methane.
- It most likely has a strong core of silicate and iron.
- Its atmosphere, more than 8000 km thick, is mainly composed of dihydrogen (85%), helium (13%) and methane (2%).
- Neptune’s blue color comes primarily from methane, which absorbs light in the red wavelengths.
- Neptune’s winds are the fastest in the solar system and reach 2000 km/h.
- The planet has a system of very fine and inconspicuous rings.
40 year old seasons
Summer has arrived in the southern hemisphere of Neptune since 2005. Scientists therefore took the opportunity to study the evolution of temperatures after the austral summer solstice.
You should know that, like the Earth, Neptune has seasons when it revolves around the Sun. However, a Neptune season lasts about 40 years, a Neptunian year lasts 165 Earth years.
The researchers measured Neptune’s temperature from all the images taken over the past two decades by the thermal cameras of space and ground telescopes. They thus analyzed the infrared light emitted by the stratosphere of the planet, which enabled them to draw up a table of the temperature of Neptune and its variations during part of its austral summer.
Images of Neptune captured by the Very Large Telescope and by Hubble
Photo: ESO/P. Weilbacher (AIP)/NASA, ESA, and MH Wong and J. Tollefson (UC Berkeley)
The data collected show that, despite the arrival of the austral summer, the vast majority of the planet has gradually cooled over the past two decades. Thus, the global average temperature of Neptune fell by 8°C between 2003 and 2018.
This change is unexpected
explains Michael Roman, a postdoctoral fellow at the University of Leicester, in the United Kingdom. As we observed Neptune at the start of its southern summer, we expected temperatures to warm slowly, not cool.
Additionally, astronomers were surprised to discover a dramatic warming of Neptune’s south pole over the past two years of observations. Temperatures there rose rapidly by 11°C between 2018 and 2020.
Although Neptune’s warm polar vortex has been known for many years, such rapid polar warming has never been observed before on this planet.
note the researchers, whose details of the work are published in The Planetary Science Journal (New window) (in English).
Difficult to explain
Astronomers do not yet know how to explain Neptune’s temperature variations.
They could be due to changes in the chemistry of Neptune’s stratosphere, random weather phenomena, or even the solar cycle.
they say.
More data will be collected over the next few years and may help explain these fluctuations.
Future telescopes, such as the European Giant Telescope and the James Webb Space Telescope, will allow us to observe temperature changes in more detail, but also to better understand the chemistry and temperature of Neptune’s atmosphere.
” I think Neptune itself is very intriguing to many of us, because we still know very little about it. »
All of this hints at a more complex picture of Neptune’s atmosphere and how it changes over time.
he explains.
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