Getting a glimpse inside the moon

December 18, 2018

New research from University of Alberta physicists provides the first-ever model of our Moon's rotational dynamics, taking into consideration its solid inner core. Their model helps to explain why, as seen from Earth, the Moon appears to wobble on its axis.

The answer, said physicist Mathieu Dumberry, lies in the complex geometry of the Moon's orbit, locked in what is known as a Cassini state.

"The Moon goes around the Earth, but its orbit is inclined by about five degrees with respect to the normal to the ecliptic plane, the plane about which Earth rotates around the Sun. But just like the Earth's rotation axis is inclined by 23.5 degrees in space, the Moon's rotation axis is also inclined, by about 1.5 degrees," explained Dumberry, associate professor in the Department of Physics. "Over one orbit, it points at the same direction in space--which is in the same plane as the normal to the orbit of the moon. This defines a Cassini state."

This type of lunar orbit was first observed by Giovanni Cassini more than four centuries ago. Since that time, the complex mathematical and physical elements of the Cassini state have been examined by scientists around the world. But what makes this model unique is accounting for a solid inner core at the centre of the Moon.

The heart of the matter

"Essentially, we took all forces into account and tried to predict the angle of the inner core of the Moon," explained Dumberry. "The tilt angle can be predicted, but we need to know accurately the deep interior structure on the Moon. However we know it is not aligned with the mantle or the fluid core. We determined that the inner core is tilted as much as 17 degrees away from the mantle in one direction or 33 degrees away in the other."

And, if scientists can identify the angle of the inner core, they will be able to develop a more accurate picture of the interior of the Moon.

"This is the first model of the rotational dynamics of the Moon that fully takes into account the presence of a solid inner core," said Christopher Stys, graduate student who conducted this research under the supervision of Dumberry. "Understanding the composition of the Moon's interior may provide insight to the events leading up to the formation of the Moon and the early history of the Earth."
The paper, "The Cassini State of the Moon's Inner Core," was published in the Journal of Geophysical Research: Planets(doi: 10.1029/2018JE005607).

University of Alberta

Related Moon Articles from Brightsurf:

New mineral discovered in moon meteorite
The high-pressure mineral Donwilhelmsite, recently discovered in the lunar meteorite Oued Awlitis 001 from Apollo missions, is important for understanding the inner structure of the earth.

First measurements of radiation levels on the moon
In the current issue (25 September) of the prestigious journal Science Advances, Chinese and German scientists report for the first time on time-resolved measurements of the radiation on the moon.

Researchers develop dustbuster for the moon
A team led by the University of Colorado Boulder is pioneering a new solution to the problem of spring cleaning on the moon: Why not zap away the grime using a beam of electrons?

First global map of rockfalls on the Moon
A research team from ETH Zurich and the Max Planck Institute for Solar System Research in Göttingen counted over 136,000 rockfalls on the moon caused by asteroid impacts.

Going nuclear on the moon and Mars
It might sound like science fiction, but scientists are preparing to build colonies on the moon and, eventually, Mars.

Astronaut urine to build moon bases
The modules that the major space agencies plan to erect on the Moon could incorporate an element contributed by the human colonizers themselves: the urea in their pee.

How moon jellyfish get about
With their translucent bells, moon jellyfish (Aurelia aurita) move around the oceans in a very efficient way.

Does crime increase when the moon is full?
Noting that anecdotal beliefs can affect public policies and practices, a 'pracademics' team from NYU's Marron Institute of Urban Management worked with public safety personnel to examine the commonly held axiom that crime rises with the full moon -- and found that the evidence is just not there.

Soil on moon and Mars likely to support crops
Researchers at Wageningen University & Research in the Netherlands have produced crops in Mars and moon soil simulant developed by NASA.

Are we prepared for a new era of field geology on the moon and beyond?
Space agencies must invest more resources on field geology training of astronauts to take full advantage of scientific opportunities on the moon and other planetary bodies, Kip Hodges and Harrison Schmitt urge, in an Editorial.

Read More: Moon News and Moon Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to