The mission of the James Webb Space Telescope is to study the most distant and earliest galaxies in the universe.
Oscar del Barco Novillo , University of Murcia
Just a few days after showing us the new infrared images of the planet Mars, the James Webb Space Telescope surprises us again with some extraordinary snapshots. This time it is Neptune’s turn.
This frozen planet owes its name to the Roman god of the sea because of the intense blue color with which it is observed in visible light. The reason for this bluish hue is the presence of methane in its atmosphere. This chemical compound absorbs a large amount of red light from the Sun, and it is the blue color that is mostly reflected by the planet.
Since the mid-19th century, astronomers have suspected the existence of a planet further away than Uranus, because the latter’s orbit was disturbed by a massive star not yet discovered by astronomical observations.
It was on September 23, 1846 that the German astronomer JG Galle found Neptune in the exact position where the French mathematician Le Verrier had predicted through mathematical calculations.
The image above shows, for comparison, three images of this beautiful icy giant recorded by two space telescopes (the Hubble and the James Webb) and the Voyager 2 space probe (the latter, after a 12-year journey to the blue Planet).
It is worth mentioning that the image of Neptune taken by the James Webb is not bluish because this telescope captures the infrared radiation emitted by said planet.
Some facts about Neptune
It is the eighth planet in order of increasing distance from the Sun: sunlight takes about 4 hours to reach this icy giant, being 30 times farther from the Sun than the Earth is.
Although its bluish color catches our attention, this planet receives very little solar radiation, so it is relatively dark: noon on Neptune would be equivalent to a dim sunset on our planet.
With a mass 17 times that of the Earth and a volume of almost 58 Earths, its average density is 3.4 times less than that of our planet (similar to that of table sugar ). This data refers to the non-rocky nature of the ice giant.
A day on Neptune lasts about 16 hours, due to its high speed of rotation. However, the blue planet orbits the Sun in about 165 Earth years: this means that Neptune has only completed one revolution around the Sun since it was discovered in 1846.
A turbulent atmosphere containing clouds of methane
The Neptunian atmosphere is composed mainly of hydrogen (84%), helium (12%), and methane (2%), in addition to other compounds such as ammonia. It has a band structure similar to that of Jupiter or Saturn.
It is divided into two fundamental regions: the troposphere (or interior region, where the temperature decreases with height) and the stratosphere (the upper region, with a thermal behavior opposite to the previous one).
The atmosphere of the blue planet is very active and turbulent: giant hurricanes (with an extension similar to the Earth) and supersonic methane winds have been recorded. Their speeds reach up to 2,000 kilometers per hour and are the most intense in the entire Solar System.
It also has a ring system
Like other outer planets in the Solar System, the blue giant also has a ring system . Formed mainly by ice and silicate particles, their color is very dark and they are difficult to observe.
The five main rings are named after the most relevant astronomers in the study of this planet: from the outermost to the innermost they are called the Adams, Arago, Lassell, Le Verrier and Galle rings.
It was precisely the Voyager 2 space probe that demonstrated the existence of the Neptunian rings when it passed near the icy giant in 1989.
its natural satellites
To date, 14 satellites of Neptune are known . Triton is the largest by far.
Discovered just 17 days after Neptune by amateur astronomer William Lassel , Triton is one of the coldest bodies in the Solar System (its mean surface temperature is about 235 degrees Celsius below zero).
Formed by a crust of frozen nitrogen on a mantle of ice, Triton is the only large satellite whose orbit is retrograde : this means that its direction of rotation around Neptune is opposite to the rotation of the planet.
Other inner satellites (whose orbits are practically circular and photographed by the James Webb Space Telescope) are Naiad, Thalassa, Despina, Galatea, Larissa and Proteus.
The new infrared images of this frozen world
As we discussed earlier, the James Webb operates in the infrared range, so it cannot reproduce the typical bluish color of the planet.
Analyzing the image above in detail, we can distinguish the following characteristics of Neptune:
- High-altitude methane ice clouds: Shown as bright streaks and dots. These clouds strongly reflect sunlight before the infrared radiation is absorbed by methane gas.
- The atmospheric circulation that generates the winds and storms on Neptune: a faint, thin bright line can be seen encircling the planet’s equator. In this warmer region, the Neptunian atmosphere emits more infrared radiation than the surrounding cooler atmospheric gases.
- High cloud bands around the Neptunian North Pole: Shown in a bluish hue, they occupy a large region in the northernmost parts of the planet.
- Neptune’s rings: Perhaps the most striking (and possibly the most beautiful) feature of the new James Webb images. In addition to several rings of varying brightness and size, the fainter dust lanes of the icy giant can be clearly distinguished.
On the other hand, the James Webb also captured seven of Neptune’s 14 known moons: Naiad, Thalassa, Despina, Galatea, Larissa, and Proteus.
And the bright point of light in the shape of an eight-pointed star? It is not a star but the Neptunian satellite Triton, the largest, which intensely reflects sunlight. The starry shape is due to diffraction from the James Webb primary mirror .
Importance of these new images
These spectacular snapshots once again demonstrate the great ability of the James Webb to record images in the infrared range. In the case of the planet Neptune, the faintest rings had been practically hidden for more than 30 years (when the Voyager 2 space probe approached this icy giant).
Let us not forget that the main task of the James Webb Space Telescope is, among others, the study of the most distant and primitive galaxies in the universe, as well as the investigation of the atmospheres of extrasolar planets.
However, we cannot help but be amazed and admire these new images of Neptune that provide us with a new way of looking at this beautiful icy giant.
Oscar del Barco Novillo , Associate Professor in the area of Optics, University of Murcia
This article was originally published on The Conversation . Read the original .