2019-04-20_New_Scientist

20 April 2019 | NewScientist | 19

Volcano flows are

a load of hot air

THE rocky debris and superheated

steam that erupts out of volcanoes

can travel over land at around

200 kilometres per hour. These

pyroclastic flows may be so speedy

because the rubble surfs on a

pocket of air that builds up

underneath the flowing rocks.

To simulate these flows, Gert

Lube at Massey University in New

Zealand and his team dropped

volcanic rock and ash into a chute

with heat-resistant glass sides.

The rocks at the top passed through

a fiery portal heated to up to 130°C,

so the debris simulated a volcano’s

superheated ash.

The team found a feedback loop

that determines the speed of the

flow. When a pyroclastic flow moves

slowly, the air between the ash and

rock has the highest pressure near

the ground, which shoves rock

particles together and pushes gas

upwards, slowing down the rubble.

But if it is moving quickly, the region

of highest pressure within the flow

lifts off the ground.

As a result, the low pressure

at the bottom of the flow draws

air downward, and the volcanic

material packs together and traps

the gas beneath it. This creates an

air pocket that the rocks coast on as

they cover uneven ground or climb

inclines, which makes them more

dangerous (Nature Geoscience,

doi.org/c4c7).

Flying cars could be green

A FUTURE generation of flying cars

could upend the idea that all flying is

bad for the climate.

Firms such as Rolls Royce, Lilium

and Vertical Aerospace have argued

that flying cars could be a green

mode of transport, despite the large

amounts of energy they need to

get off the ground. One of the first

studies into the environmental

impact of such vertical take-off and

landing (VTOL) vehicles suggests

that their backers could be right –

at least in some circumstances.

Gregory Keoleian at the University

of Michigan and his colleagues found

that VTOLs, if they ever take to the

skies, would produce 6 per cent less

emissions than an electric car over

a 100-kilometre journey (Nature

Communications, doi.org/c4c6).

Don’t jump into a VTOL just yet,

though. The difference was only

very small and there are several big

catches. Number one being that

flying cars don’t really exist yet –

they are only at the prototype stage.

Moreover, aerial journeys shorter

than 35 kilometres would produce

more emissions than electric cars,

because of the energy required

at take-off.

Dust storms on Mars aren’t all

about dust – they are also full of

water. A satellite orbiting Mars

has taken the most detailed

measurements yet of how these

rare events trap water, which may

help reveal what happened to the

water that used to be abundant

on the Red Planet.

In 2018, the largest recorded

dust storm circled the entire

Martian globe so thickly that it

hid the surface from the sun and

killed the Opportunity rover.

The ExoMars Trace Gas Orbiter

watched this cataclysmic storm

from orbit. Just before sunset

and just after sunrise on Mars,

it examined the atmosphere to

determine how the dust storm

absorbed sunlight.

Ann Carine Vandaele at the

Royal Belgian Institute for Space

Aeronomy and her colleagues

used this data to determine how

water was behaving in the storm.

They found that just before the

storm, there were water ice clouds

in the atmosphere, but no water

vapour more than 40 kilometres

above the surface. This changed a

few days later when water vapour

appeared at altitudes of 40

and 80 kilometres, seemingly

replacing the water ice clouds

(Nature, doi.org/gfzbdr).

This probably occurs because

the dust absorbs heat, warming

up the atmosphere and making

it circulate more strongly, which

prevents the formation of ice

clouds, says Vandaele.

The dust storms puff up the

atmosphere, making it easier for

gases including water vapour to

escape into space, so this could

help to explain how Mars became

so inhospitable.

Large dust storms helped Mars become dry

Say no to Planet

McPlanetface

A DWARF planet discovered over

a decade ago is the largest body

we know of in our solar system

without a proper name – but that

is about to change.

Megan Schwamb, an

astronomer at Gemini

Observatory in Hawaii, and her

colleagues have opened a public

vote to name the world, which is

currently known only as 2007

OR10. They have selected three

options that fit the International

Astronomical Union’s rules on

official names for minor planets:

Gonggong, a Chinese water god

who caused floods and chaos;

Holle, a winter fertility spirit

from European folklore; and Vili,

a Nordic god and brother of Odin.

Why name it now, instead of

when the researchers discovered

OR10 in 2007? “You can’t name

something when you don’t know

anything about it,” says Schwamb.

“When we found it, I knew the

orbit and generally the size.”

Now, after lots of follow-up

observations, we know that its

surface is covered in water ice,

with traces of methane ice. When

sunlight hits the methane ice,

it turns red, which may be why

OR10 is one of the reddest rocks

in the distant Kuiper belt.

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