Massive yet compact galaxies discovered relatively near the Milky Way belong to a type believed extinct since the early history of the universe, astronomy.com said.
Astronomers using NASA's Galaxy Evolution Explorer (GALEX) satellite report finding dozens of small, massive galaxies 2 to 4 billion light-years away.
The newly found galaxies appear to be teeming with exploding supernovae and hot, young stars--two hallmarks of galactic youth. The astronomers estimate the galaxies span ages from perhaps as little as 100 million years to a billion years, making them newborns in galactic terms. The Milky Way is about 10 billion years old.
Says Tim Heckman of John Hopkins University, head of the team making the discovery, "These galaxies differ from mature galaxies like our own Milky Way by being extremely bright in ultraviolet light, and also by being quite compact."
The discovery surprised the researchers because it told them today's universe is still spawning massive, compact galaxies. "We knew there were really massive young galaxies eons ago," says Chris Martin of Caltech, principal investigator for GALEX. "But we thought they had all matured into older ones like the Milky Way."
The newly discovered galaxies are fossils in another way, too. They're comparatively free of the heavy elements needed for making planets and life. Heckman says, "The chemical properties of these newborn galaxies are consistent with the young galaxies from 10 billion years ago."
This differs markedly from the Sun and planets, which represent a second-generation (or later) stage of star birth in the Milky Way. The heavy elements making up the solar system were forged in older, massive stars that scattered their debris into the galaxy ages ago.

High-resolution images from the Mars Express spacecraft reveal the planet's largest volcanoes may have seen activity--volcanic and glacial--in the past few million years.
Lava erupted on the flanks of the large martian volcano Olympus Mons perhaps only 2.4 million years ago, says a team of planetary scientists who examined sharply detailed images of five martian volcanoes in Tharsis. The images were taken by the Mars Express spacecraft's High Resolution Stereo Camera (HRSC).
"These volcanoes are potentially still active today," says Gerhard Neukum of Germany's Freie Universit?t Berlin, team leader and the HRSC's principal investigator. Moreover, team members say, glacial deposits 4 million years old ring the base of Olympus Mons. Their report appears in the December 23-30, 2004, issue of Nature.
To date the surfaces, the scientists counted craters on the five volcanoes and their immediate surroundings, then scaled the results to studies of Earth's Moon. The most-uncratered, hence youngest, area seen - 2.4 million years old - lies on the western flank of Olympus Mons. (Besides the Mars Express photos, the area was also caught in frame E10-00828 by the orbiting Mars Global Surveyor's camera.)
Surrounding Olympus Mons lie features resembling rock-covered glaciers and debris flows. By counting craters on these surfaces, the researchers dated the major flow lobes at 130 to 280 million years old, with lesser areas being 20 to 60 million years old. A few small locations dated to about 4 million years.
Running down from the scarp that circles Olympus Mons are rocky "tongues" of debris with no craters at all on them. "These are so young," the team says, "that they cannot be reliably dated."
The young ages arouse questions for some scientists. Mark Robinson of Northwestern University says, "The 2-million-year-old surface may be a lava flow that occurred then. However, it could also be a landslide that occurred 2 million years ago, or perhaps glacial modification."
Sand dunes, Robinson explains by way of example, can bury a fresh lava flow and protect it from being cratered for tens of million of years. If unearthed, it will have the appearance of having flowed recently. Another pitfall, according to Robinson, concerns the martian cratering rate, a number he describes as very poorly known. "So caution's the word," he concludes.
Mars geologists generally agree the planet saw volcanic activity within the last 100 million years. And such activity, if it still continues in the geological present, might account for some or all of the methane observed by Mars Express. Because methane doesn't linger in the martian environment, it needs replenishment. That could be the fingerprint of recent activity.

Children tend to sleep later and later as they get older until the age of about 20.

We all know that teenagers hate to get up in the morning. But are they really just lazy, or is there a biological cause?
A European survey of the sleeping habits of 25,000 people now provides powerful evidence that biology is indeed to blame. Whereas children sleep later and later as they get older, we undergo an abrupt shift at age 20, after which we start sleeping earlier again, nature.com said.
The change is so sudden that researchers suggest it should be used to officially mark the end of adolescence.
We all go through phases of puberty and adolescence before we reach adulthood. Both periods begin when the reproductive system starts maturing.
Scientists agree that puberty ends when bone growth stops--at around 16 years in girls and 17.5 years in boys. But the end of adolescence--a concept that is part social, part psychological and part physiological--has always been less well defined.
Our sleep and wake phases are regulated by an internal body clock. Each cycle runs at about 24 hours, but the exact timing varies from individual to individual. People with particularly early cycles, called "larks", tend to go to bed early and wake up early, whereas those with a late cycle ("owls") tend to be more active at night and sleep later in the morning.
To investigate how this "chronotype" varies throughout life, Till Roenneberg from the University of Munich, Germany, and his colleagues asked 25,000 people, aged between 8 and 90, a series of questions about what time they go to sleep and wake up.
From this, the researchers calculated the average "mid-point" of each person's sleep--in other words, the time half way between when they go to sleep and when they wake up--on days when they had no work obligations.
When they plotted the mid-points against each person's age, the researchers found that children tend to sleep later and later as they get older until the age of about 20. At that age, there is an abrupt shift in sleeping habits, and the sleep mid-point starts getting earlier and earlier again.
Roenneberg says he can't prove that the shift is caused by behavioural or environmental factors. "Do teenagers sleep late because they go to the disco, or do they go to the disco because they sleep late?" he asks.
But he believes that the abrupt timing of the shift suggests a biological cause. "This is the first time that we have been able to trace the end of adolescence," he says.
He points out that the timing of the shift also reflects the general trend of females to develop earlier than males. The women in the study that slept latest were 19.5 years of age, whereas the men's sleep got later and later until 20.9 years.
"An objective marker like this could be very helpful in a range of disease conditions," says Russell Foster, a chronobiologist at Imperial College, London. Mental disorders such as schizophrenia and bipolar diseases are often accompanied by delayed sleep phases, he points out.
He suggests it could be worth investigating whether changes in the timing of this shift could be used to spot the development of such disorders early on.