SKY_July2014.pdf

Newsnotes

New images from ESA’s Venus Express

orbiter show three transient bright spots

at the edge of a young rift zone, hinting

there might be active volcanoes on Venus

today. Estimates based on the new data

suggest the spots are 980°° to 1520°F (527°

to 827°C), well above the planet’s typical

balmy temperature of about 870°F, Eugene

Shalygin (Max Planck Institute for Solar

System Research, Germany) and col-

leagues reported March 17th at the Lunar

and Planetary Science Conference in The

Woodlands, Texas.

The team analyzed images from 36

spacecraft passes over a region surround-

ing Maat Mons, a giant shield volcano that

scientists think erupted 10 to 20 million

years ago. After considering whether they

PLANETS I Volcanoes on Venus?

were seeing image artifacts or holes in the

clouds, they rejected both theories. Instead,

the researchers think the bright spots could

be ongoing lava fl ows stretching 25 km or

so, a chain of cinder cones, or volcanic hot

spots — any of which would provide proof

that Venus is active today.

So far the claim has not been con-

fi rmed. There’s no evidence of past lava

fl ows in this area, and there’s a 3-month

gap in coverage after the features were

spotted. Shalygin’s team plans to sift

through archived radar images from

NASA’s Magellan spacecraft (which visited

the planet from 1990 to 1994) and also

to look for similar hot spots in other rift

zones using Venus Express. ✦

■ SHANNON HALL

Astronomers have known for more than

a century that Jupiter’s signature feature,

its Great Red Spot, has been shrinking. In

the late 19th century the spot was nearly 35°

wide, which corresponds to about 40,

kilometers, or more than three times

Earth’s diameter. By 1979, when Voyagers

1 and 2 fl ew past Jupiter at close range,

the longitudinal extent had shrunk to 21°

(25,000 km), though its top-bottom width

(12,000 km) was essentially unchanged.

This contraction has continued, and

now the iconic vortex is smaller than ever

before. According to John Rogers (British

Astronomical Association), during the

planet’s recent apparition in 2013–14 the

Red Spot spanned just 13.6° in latitude, a

JUPITER I Not-So-Great Red Spot

Historic Occultation Goes Unseen.

Would-be observers of Regulus’s occulta-

tion by asteroid 163 Erigone on March

20th were clouded out — everywhere.

Read more about why no one saw Regu-

lus wink out at skypub.com/regulusfl op.

Mercury Really Did Shrink. Geophysi-

cists using images from NASA’s Messen-

ger spacecraft have updated estimates

of how much the Iron Planet shrank as

it cooled after forming 4½ billion years

ago. The newly calculated shrinkage

— between 3.7 and 7.1 km — matches

theoretical predictions and resolves a

decades-old disagreement between previ-

ous estimates and theory. Interestingly,

the widespread volcanic plains near Mer-

cury’s north pole bear a disproportionate

share of the wrinkle ridges and thrust

faults. These plains cover only 6% of the

planet, yet 28% of the counted features

are found there, and they account for 19%

of the total shrinkage, report Paul Byrne

(Carnegie Institution) and colleagues

March 16th in Nature Geoscience. The

team also found several instances where

the regional topography slowly undulates,

as if the crust buckled on larger scales.

■ J. KELLY BEATTY

Subsurface Ocean Confi rmed. Long-

sought evidence of a subsurface ocean

on Saturn’s moon Enceladus has fi nally

solidifi ed. Scientists suspected that a

reservoir of liquid water feeds the vapor

and water-ice crystals that the little moon

spews from its south pole, creating Sat-

urn’s delicate E ring. Using the changes

in Enceladus’s gravitational tug on

NASA’s Cassini spacecraft as the orbiter

fl ew by the moon, Luciano Iess (Sapienza

University of Rome, Italy) and colleagues

suggest a body larger than Lake Superior

lies 30 to 40 km beneath the moon’s icy

south pole. The subsurface ocean might

exist thanks to tidal stresses from Saturn,

the team reports in the April 4th Science.

Jupiter’s Europa likely has a subsurface

ocean for similar reasons.

■ SHANNON HALL

IN BRIEF

length of only 15,900 km.

Meanwhile, the spot’s rotation con-

tinues to vary a lot. The Voyagers found

a period of 6 to 8 days, corresponding to

mean wind velocities around the rim of

120 meters per second (270 mph). In 2000,

NASA’s Galileo orbiter looked on as the

Great Red Spot raced around at a record-

setting 165 m/sec. This past year observ-

ers found a period of just 3.6 days, and the

outer winds clocked at 144 m/sec.

No one knows what’s causing these

changes, but Rogers suspects the storm

is gaining rotational energy as it feeds on

smaller spots swept along by the northern

jet stream of the South Temperate Belt.

■ J. KELLY BEATTY

16 July 2014 sky & telescope

Jupiter’s Great Red Spot appears much larger in this drawing from 1881 by Thomas Gwyn

Elger (left) than it does in this photo from 2014 by Christopher Go. South is up.