Can moons have moons?

A new study shows that Earth’s moon should, theoretically, be able to have its own moon. Why doesn’t it?

Size comparison of the major moons in our solar system 

Most of the planets in our solar system have orbiting moons, and even some asteroids have their own moons. But do any moons have moons? Is it possible? Could there be so-called submoons?

It’s a simple enough question. If most other objects in the solar system can have moons, why not moons themselves? Researchers decided to try to answer this question of a 4 year old. Their results have now been published in a new peer-reviewed paper in the February 2019 issue of the Monthly Notices of the Royal Astronomical Society.

Planets orbit stars and moons orbit planets, so it is natural to ask if smaller moons could orbit larger ones. So far at least, no submoons have been found orbiting any of the moons considered most likely to support them – Jupiter’s moon Callisto, Saturn’s moons Titan and Iapetus and Earth’s own moon.

The lack of known submoons in our solar system, even orbiting around moons that could theoretically support such objects, can offer us clues about how our own and neighboring planets formed, about which there are still many outstanding questions.

Earth’s moon should theoretically be able to have its own moon. Why doesn’t it?

Researchers found that only large moons on wide orbits from their host planets would be capable of hosting submoons. Usually, any submoons orbiting smaller moons closer to their planet would have their orbits destabilized by tidal forces. Jupiter’s large moon Callisto, Saturn’s large moon Titan, another Saturn moon called Iapetus and Earth’s moon could all theoretically have submoons, so why don’t they?

There may be other sources of submoon instability, such as the non-uniform concentration of mass in Earth’s moon’s crust.

Part of the answer might also have to do with how the primary moons formed in the first place. Earth’s moon is thought to have been born out of a collision between Earth and another body about the size of Mars – and that collision may have helped life on Earth to get started. But some other moons, like those orbiting Jupiter and Saturn, originated from the same cloud of gas and dust that the planets themselves formed from.

Even asteroids can have moons, such as 2004 BL86. It is about 325 meters in diameter, and its moon is tiny, only 70 meters wide.

It may be that in many or even most cases, there are multiple factors that make the orbits of submoons inherently unstable. Knowing whether that is true or not may have to wait for discoveries of moons orbiting distant exoplanets. Moons themselves are much harder to detect and only one promising candidate has been found so far – a possible exomoon orbiting the Jupiter-sized exoplanet Kepler-1625b. That possible moon – about the size of Neptune – is large enough and far enough from its planet that submoons should be possible as well. Astronomers will need to verify that primary moon first – if it does exist – before looking for any submoons.

Even though Earth’s moon doesn’t have a submoon now, it may in the future, according to the researchers – an artificial one, perhaps NASA’s planned Lunar Gateway. The Lunar Gateway would help to establish humanity’s presence in deep space.

The possibility of moons having their own moons is a fascinating one, even though we haven’t found any examples yet. This new research from Carnegie Science shows that it is indeed possible, but only under the right circumstances.

Download the research paper here.

Adapted from EarthSky.org

In this Tokyo cafe, the waiters are robots operated remotely by people with disabilities

A pop-up restaurant in Tokyo has run a trial employing disabled people to work as waiting staff. But this is no ordinary trial. Instead of taking orders or clearing tables themselves, the staff of the Dawn ver.β cafe were piloting a team of robots from the comfort of their homes.

The robots were developed by Kentaro “Ory” Yoshifuji, CEO of the Ory Lab, which he set up with co-founders, Aki Yuki and Yoshifumi Shiiba. The remote-controlled OriHime-D robots are part of on an ongoing project to use technology to combat social isolation. They stand 1.2 metres tall and have expressionless, white faces reminiscent of Japanese Noh masks. They transmit video and audio back to their controllers, who are able to direct them from home via a smartphone or tablet.

The cafe is named after a similar establishment in a 2008 anime called Time of Eve, where robots and humans co-exist as equals. The addition of ver.β (beta) to the cafe’s name was there to show it was a work in progress – a beta version.

Five OriHime-D robots were used during the trial, and they were controlled by a team of 10 people, with a range of conditions including amyotrophic lateral sclerosis (ALS), the most common motor-neuron disease. They were all paid 1000 yen ($8) per hour, which is just above the minimum wage in Japan.

Even people with very limited mobility are able to interact with and control OriHime-D robots. Ory Labs has created a video showing how a man who is only able to move his eyes can still operate the robot, and another where a man in a hospital bed gets an OriHime-D to hand a cup of coffee to a waiting Yoshifuji.

Yoshifuji has an impressive track record as an inventor with an interest in using technology for good. Between the ages of 10 and 14 he did not attend school due to poor health and went on to represent Japan in the 2005 Intel Science and Engineering Fair (ISEF), with a project designed to help wheelchairs climb curbs. It was the years he spent missing out on school that ultimately led to the development of OriHime, which he sees as a way to help people overcome adversity and disability to actively participate in society through the use of avatars.

There are 75 million people in the world who need a wheelchair but only 5% to 15% of those in need actually have access to one. Globally, there are an estimated 200 million visually impaired people and 466 million people with hearing loss who aren’t able to access help. But in recent years, the topic of assistive technology has started to attract more attention.

While there are still many accessibility barriers technology can be used to break down, the use of robots is already underway in some situations. The Shin-tomi nursing home in Tokyo has around 20 different robots in use performing different aspects of residents’ care, from leading exercise sessions to powering interactive soft toys.