TalkPHP - Adding Timestamps in SQL?

Okay, this should be stupidly easy, but I can't figure it out :(

I have this table in my database:

PHP Code:


		
			
CREATE TABLE IF NOT EXISTS `articles` (

  `id` int(10) unsigned NOT NULL auto_increment,

  `release_date` timestamp NOT NULL default CURRENT_TIMESTAMP,

  `title` varchar(100) NOT NULL,

  `content` longtext NOT NULL,

  `link` varchar(100) NOT NULL,

  `author_id` int(10) unsigned NOT NULL,

  PRIMARY KEY  (`id`),

  KEY `release_date` (`release_date`,`author_id`),

  FULLTEXT KEY `title` (`title`,`content`)

) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=5 ;

I'm trying to set the release date when I post a new article like this (using PDO to access a MySQL database):

PHP Code:


		
			
//    Construct our timestamp.    

$theTimestamp = mktime( 0, 0, 0, $_POST['month'], $_POST['day'], $_POST['year'] );

$theStatement = $theDatabase->prepare( <<<_SQL_

    INSERT INTO `articles` 

    ( `release_date`, `title`, `content`, `author_id` )

    VALUES ( ?, ?, ?, ? )

_SQL_

    );

            

$theStatement->execute( array($theTimestamp, $_POST['title'], $_POST['content'], $theSession['user_id'] ) );

Whenever I run this piece of code the timestamp ends up being stored in my table as 00000000000... (i.e. Wed 31st Dec 1969 ).

I have a section of code that previews the article and constructs the timestamp in exactly the same way and that works fine. Shouldn't this just work? What am I missing here?