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The Juno spacecraft arriving at Jupiter this morning will investigate, among other things, whether the giant planet has a core

Its planned orbit will be very elliptical and it will bring it close to the poles - an altitude of about 4,300 km and up to the orbit of Callisto, the most distant large moon of Jupiter - that is, to an altitude of 1.9 million km.

Visualization of the Juno spacecraft approaching Jupiter. From the NASA Twitter account
Visualization of the Juno spacecraft approaching Jupiter. From the NASA Twitter account

The Juno spacecraft arrives today (July 5 at around 05:15 am) to Jupiter, its planned orbit will be very elliptical and it will bring it close to the poles - an altitude of about 4,300 km and up to the orbit of Callisto, the most distant large moon of Jupiter - that is, to the altitude of 1.9 million km.

The orbit was designed so that the spacecraft would avoid too long contact with Jupiter's radiation belt, but would still allow it to perform close-up studies of the polar atmosphere, magnetosphere and gravitational field. The spacecraft will spend over a year and a half (until February 2018, if it is not decided to extend its operation). It circled Jupiter 37 times with the duration of each orbit being 14 days.

In fact, Juno has already begun investigating Jupiter's magnetic field after on June 24th it passed through the shock wave at the entrance to Jupiter's magnetosphere, and then crossed a low-density region of the magnetosphere. In doing so, it moved from the environment characterized by the solar wind to the one dominated by Jupiter's magnetosphere. Juno's instruments may provide interesting information about the sudden change in particle density.

About a year ago Prof. Royat Khaled from Tel Aviv University gave a lecture on the large gas planets - Jupiter and Saturn and the Juno spacecraft mission to Jupiter to the members of the Israel Astronomical Society. The following excerpts are taken from her lecture in a light adaptation. You can also watch the video of the lecture.

Khaled is part of the scientific team of NASA's Juno probe that will explore the planet Jupiter. She is also one of the chief scientists in the research team of the European Space Agency's Jupiter Icy Moon Explorer probe and also a research team member of the PLATO space telescope of the European Space Agency, which is supposed to be launched in 2024.

"Giant planets are important both because of their mass and because of their influence on the smaller bodies in the solar system."

Jupiter is the largest planet in the solar system, its mass is equal to 318 Earth masses and its radius is 71,492 Earth masses. In terms of chemical composition, it is more similar to a star like the Sun because it is mainly composed of hydrogen and helium, but it also contains heavy substances (in astrophysics, heavy substances are defined as those heavier than helium, that is, almost all the elements and their compounds). Heavy materials can be water, rocks, etc.

The question we ask on a daily basis is how many heavy materials we have. The other question is does the planet have a core and if so what is its composition? Rocks, maybe water? The question of the core is important because different models give different predictions and therefore the very existence of a core is important.

According to the standard theory, a gaseous planet forms around a core like any other planet, but when the mass of the core is large enough it absorbs more material and grows to be giant. According to this model we expect there to be a core in the center. The second model is called gravitational stability according to this theory there was a stable region in the pre-planetary disk, which carried hydrogen and helium around it. According to this model, no core is expected to form.

So if we can estimate the core mass of Jupiter we may be able to say how Jupiter was formed and perhaps how giant planets are formed throughout the galaxy and the universe.

Another feature of Jupiter is a very fast rotation (nine hours and 55 minutes and a half). We have very rich atmospheric dynamics - due to the fact that it is made of gas and rotates very quickly. It has strong winds, a strong magnetic field. We estimate that Jupiter is the first planet to form in the solar system and due to its massiveness it influences the formation of all other bodies in the solar system.

Another question we ask ourselves - does Jupiter have water (and therefore also oxygen). The Galileo spacecraft found no signs of water in the lower atmosphere. Is Jupiter a dry planet or is there water but it is concentrated in the center of the planet.

We also want to know how much heavy matter there is in Jupiter even if most of its composition is hydrogen and helium. The mother probably reaches 10, 20 or maybe 50 land masses. In the upper atmosphere the hydrogen is molecular. When you go further down, you get metallic hydrogen - hydrogen that behaves like a metal, and that's how Jupiter's magnetic field is created.

The beautiful colors we see in Jupiter's atmosphere originate mainly from ammonia gas. When we think that under this mantle there are also clouds of water. The turbulence in the atmosphere originates from the rapid rotation of Jupiter.

The Great Red Spot is a storm that lasts over 300 years. The huge storms also cause much stronger lightning than on Earth. They are 100 times brighter than ours. You see these stripes - moving in opposite directions and in the middle between them there is turbulence. In terms of mass this layer is meaningless but in terms of atmospheric dynamics it is very beautiful and rich.

Jupiter's magnetosphere is also the most impressive in the solar system. It reaches the orbit of Saturn. As for what is the source of the magnetic field - dynamo theories are not completely fixed but because we have metallic hydrogen spinning fast we expect there to be a very strong magnetic field. If there is a very strong magnetic field, warning aurora phenomena are created there.

It is impossible to land on it because it is a gaseous planet, but it is possible to make measurements of the magnetic field and the gravity field from space. It also doesn't have seismology unlike the Earth, so we have to think of other ways to get this information.

No device would survive inside Jupiter's atmosphere. The probe that Galileo sent also only reached a height where the atmospheric pressure was low and then it disintegrated. The ability to penetrate the atmosphere is zero.

And here we come to the Juno space mission - a NASA spacecraft that left Earth in August 2011, it will arrive in mid-2016, and will carry out a mission of one and a half years, at the end of which it will crash into Jupiter in February 2018. Juno is also the first mission to the outer solar system that uses solar energy (In all the missions so far there were nuclear reactors that produced electricity).

The reason the journey to Jupiter takes five years is not because it is impossible to get there faster, if we want the spacecraft to be caught by Jupiter's gravity and enter orbit around it, it needs to reach it at a slow speed, otherwise it will continue on.

Jupiter was visited by many spacecraft - in the seventies Pioneer 10 and 11 passed by, in the eighties it was Voyager 1 and 2. In the XNUMXs the Galileo spacecraft explored it from orbit around it and now Juno is reaching it, while in the XNUMXs the European Space Agency is expected to send the JUICE spacecraft to Jupiter.

Why do we need another spacecraft if Galileo spent many years on Jupiter?

Although Galileo studied Jupiter for many years, the difference between Galileo and Juno is in the orbital geometry. Galileo revolved around the equator. Because of this, the gravitational field could not be measured, and therefore nothing could be said about its internal structure. To measure the gravitational field we need a polar orbit - from pole to pole.

The European mission that is expected in the next decade will mainly investigate the moons that have very interesting processes, and may answer the question of whether there is water and possibly life on Europa's moon.

The spacecraft consists of several magnetometers whose job it is to measure Jupiter's magnetic field. You can also see that the solar collectors are very large. As we move out to 5 AU we need a lot of space to get enough radiation.

Mission objectives.

According to Prof. Khaled, the goals of the mission can be divided into four main topics:

  • Formation - determining the ratio between hydrogen and oxygen (actually determining the amount of water). Core mass information to understand how Jupiter formed.
  • Internal model - determining the composition of Jupiter and how it changes as a function of depth. Understanding the dynamics (winds) and mapping the magnetic field and the gravity field.
  • Atmosphere - mapping atmospheric changes, and changes in the composition of the atmosphere, heat measurements. The question is whether the winds are an atmospheric phenomenon or do they reach deeper, and what we see is just a signature of a wider phenomenon.
  • Magnetosphere - investigation of the structure of Jupiter's magnetic field.

Prof. Khaled estimates that following the operation our understanding of the structure of giant gas planets will change.


More of the topic in Hayadan:

Juno comes to Jupiter this week

A new record for NASA: how to extract energy from the sun 800 million kilometers away

4 תגובות

  1. I think the last sentence should be corrected: "When we move away to 5 atmospheric units..." to astronomical units...

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